The bug submission procedure isn't working, so I'll just write it here:

If I import an image sequence, and rename it in the media pane of kdenlive, the location is lost on the next time I load kdenlive. It displays "invalid clip" if I added it to timeline.

So then I have to re-add the sequence to the media pane, making sure to only use the default label. For example: %04d.png?begin:40