I often read threads about various software applications where people have nothing but trouble, and others have a dream run. Here is my situation.

I have Kdenlive installed on two computers:
#1 is a high spec desktop (built specifically for video editing).
#2 is a laptop (relatively fast) for everyday stuff, but also as a mobile editor.

Kdenlive has recently been crashing a lot on #1. It got to the point where i have a project to do today, and I just couldn't proceed (frustration ++). So I jumped onto #2 to do the job and it has been total rock steady (not one crash, not one flicker...). Previously #1 was stable, going back a month or two (or maybe more).

Obviously the two computers are not identical, but with so many variables picking out the relevant difference is difficult without reloading each with identical steps. But a couple of things to note:
#1 is running Ubuntu Studio 13.04 (64 bit). Has a few more multi-media applications than #2. Has a Nvidia GPU. i7 3rd gen CPU
#2 is running Xubuntu 13.04 (64 bit). Has a built-in ATI GPU. i7 2nd gen CPU. More everyday apps (email etc.)
Both are running Kdenlive v0.9.6 with MLT v0.8.8-1.

The minor differences are going to be lengthy. Not sure where to start or stop.
Anyway, point to make is that the software can be incorrectly judged by the environment it runs in.

Important question thought is: why? If I can't work it out, may have to reload #1 as closely as #2.
Appreciate any suggestions.

maybe graphic drivers related? what are you using on #1, if not the proprietary Nvidia ones I'd suggest trying it

I think I may have solved it.
First I uninstalled Kdenlive and melt. When uninstalling melt (via synaptic), it had to uninstall OpenShot as well.
Then reinstalled both kdenlive and melt. So far so good.
I don't use OpenShot, but installed it only to have a look.

Have being editing another project back on #1 for about last half hour, and all running good now.

Would be interesting to see the exact version differences, to see if there is a particular version at fault here. Thanks for posting the solution you used to correct the problem.

As indicated, there are so many subtle differences that it really is a stab in the dark.
Picked up the idea on re-installing from another thread where some-one was having problems with kdenlive (this was a suggestion).
Something was out of alignment under the hood - the re-install was the equivalent of power down / power up.

Kdenlive still throws the occassional hissy fit, but generally is well behaved.