If I add a video clip taken by the Olypmus E-PM1 in FullHD Fine : 1920x1080, 60i Recording, 17Mbps
I get the Information:
Your clip does not match current project's profile.
No existing profile found to match the clip's properties.
Clip size: 1920x1088
Fps: 59.96

Why is the clip size 1920x1088???

information from ffprobe:
Duration: 00:00:42.52, start: 0.888889, bitrate: 21968 kb/s
Program 1
Stream #0.0[0x1011]: Video: h264 (High), yuv420p, 1920x1080 [PAR 1:1 DAR 16:9], 59.96 fps, 59.94 tbr, 90k tbn, 59.94 tbc
Stream #0.1[0x1100]: Audio: ac3, 48000 Hz, stereo, s16, 192 kb/s
[STREAM]
index=0
codec_name=h264
codec_long_name=H.264 / AVC / MPEG-4 AVC / MPEG-4 part 10
codec_type=video
codec_time_base=1001/60000
codec_tag_string=HDMV
codec_tag=0x564d4448
width=1920
height=1088
has_b_frames=0
sample_aspect_ratio=1:1
display_aspect_ratio=30:17
pix_fmt=yuv420p
id=0x1011
r_frame_rate=60000/1001
avg_frame_rate=58521/976
time_base=1/90000
start_time=0.888889
duration=42.509133
[/STREAM]
[STREAM]
index=1
codec_name=ac3
codec_long_name=ATSC A/52A (AC-3)
codec_type=audio
codec_time_base=0/1
codec_tag_string=AC-3
codec_tag=0x332d4341
sample_rate=48000.000000
channels=2
bits_per_sample=0
id=0x1100
r_frame_rate=0/0
avg_frame_rate=125/4
time_base=1/90000
start_time=0.888889
duration=42.528000
[/STREAM]


I tried to create a new profile without success:
Size: 1920x1080
Frame rate: 60000/1001
Pixel aspect ratio: 1/1
Display aspect ratio: 16/9
Colorspace: ITU-R 709 ???
Interlaced

I guess I have to change to 1920x1088 but why?
Is the Colorspace correct?

1088 is divisible by 16, 1080 isn't. Certain h264 encoders only work in modules of 16 rows. Canon 7D, T2i and Nikon HDSLRs all encode 1088 rows off the sensor. But you'll notice that 1920x1080 is mentioned for display.

At decompression for editing or playback some codecs like Apple Quicktime crop the 8 rows off, others like CoreAVC give the option in the preferences, ffmpeg gives you what is there in the video stream 1088 in this case.

In kdenlive if I understand correctly MLT silently crops the bottom 8 rows off back to 1080. But kdenlive still gives the 'unhelpful' profile mismatch dialogue. You can turn this off in kdenlives menu under Settings. I do as much of my source is Canon h264 files.

If you create a 1088 project, there will be either 8 rows of black or 1080 cropped will be scaled vertically by the 8 pixels to 1088, not sure which kdenlive / MLT does but either way it's unwanted.

All you need to use is a 1920x1080 60i (interlaced) project already available I think and switch off the helpful message.

re colorspace, you can use mediainfo an OSS app to give you a bit more info as to the color matrix. Which is the only really important bit. Color space will be rec709 / sRGB primaries and transfer but color matrix could be BT709 or BT601.

The color matrix only matters with regard to correct color hues when converting to RGB. As kdenlive / MLT convert to RGB for color processing filters / effects and preview then getting the color matrix right stops a subtle color shift. For example pinks shift to more of an orange if BT709 is used on BT601 color matrixed sources.

Output of mediainfo:

Video
Count : 201
Count of stream of this kind : 1
Kind of stream : Video
Kind of stream : Video
Stream identifier : 0
ID : 4113
ID : 4113 (0x1011)
Menu ID : 1
Menu ID : 1 (0x1)
Format : AVC
Format/Info : Advanced Video Codec
Format/Url : http://developers.videolan.org/x264.html
Commercial name : AVC
Format profile : High@L4.0
Format settings : 2 Ref Frames
Format settings, CABAC : No
Format settings, CABAC : No
Format settings, ReFrames : 2
Format settings, ReFrames : 2 frames
Format settings, GOP : M=1, N=15
Internet media type : video/H264
Codec ID : 27
Codec : AVC
Codec : AVC
Codec/Family : AVC
Codec/Info : Advanced Video Codec
Codec/Url : http://developers.videolan.org/x264.html
Codec profile : High@L4.0
Codec settings : 2 Ref Frames
Codec settings, CABAC : No
Codec_Settings_RefFrames : 2
Duration : 42543
Duration : 42s 543ms
Duration : 42s 543ms
Duration : 42s 543ms
Duration : 00:00:42.543
Bit rate mode : VBR
Bit rate mode : Variable
Bit rate : 20821549
Bit rate : 20.8 Mbps
Maximum bit rate : 22529024
Maximum bit rate : 22.5 Mbps
Width : 1920
Width : 1 920 pixels
Height : 1080
Height : 1 080 pixels
Pixel aspect ratio : 1.000
Display aspect ratio : 1.778
Display aspect ratio : 16:9
Frame rate : 29.970
Frame rate : 29.970 fps
Frame count : 1275
Resolution : 8
Resolution : 8 bits
Colorimetry : 4:2:0
Color space : YUV
Chroma subsampling : 4:2:0
Bit depth : 8
Bit depth : 8 bits
Scan type : Interlaced
Scan type : Interlaced
Scan order : TFF
Scan order : Top Field First
Interlacement : TFF
Interlacement : Top Field First
Bits/(Pixel*Frame) : 0.335
Delay : 888.889
Delay : 889ms
Delay : 889ms
Delay : 889ms
Delay : 00:00:00.889
Delay, origin : Container
Delay, origin : Container
Stream size : 110726394
Stream size : 106 MiB (95%)
Stream size : 106 MiB
Stream size : 106 MiB
Stream size : 106 MiB
Stream size : 105.6 MiB
Stream size : 106 MiB (95%)
Proportion of this stream : 0.94812
Buffer size : 3072128 / 3072128

To clarify the settings for kdenlive:
Size: 1920x1080
Frame rate: 60000/1001
Pixel aspect ratio: 1/1
Display aspect ratio: 16/9
Colorspace: ITU-R 709
Interlaced

Couldn't find a default profile. Only 1080p_60_fps or 1080i_30_fps...
Still not sure about the colorspace... Is ITU-R 709 correct?
Thank you.

The color space will be ITU-R 709 as it's not declared otherwise.

Your mediainfo output, that's for the native source media? As there is no mention of 1920x1088 stream size. Not that it really matters re my previous comment about cropping.

Hope this solves your problem.

Thank you.
The output ffprobe and mediainfo are from the same raw file... strange!
ffprobe - Heigth=1088 - 59.96fps
mediainfo - Height=1080 - 29.970

Out of the two I'd trust the mediainfo, especially if you still have problems after setting up this profile, could be that ffmpeg is buggy in this regard.