Although its crashed on all the machines I had tried (3), they had all been 64 bit Gentoo with NVidia graphics cards.
So I just tried something totally different. A Intel Atom based machine running 32 bit Gentoo and using the onboard 950 graphics chip.

Still crashes as soon as I touch the slider to crop from the top :-(

If anyone finds crop stable, perhaps they can they comment on the spec of their system.

Yes, it is another, easier way to trigger the bug; and I will have another look at it in the next evenings; but why are you selecting the clip monitor to adjust the crop?

just compiled now this crop issue is fixed! thank you DD!

I confirm this. Compiled kdenlive from svn and mlt from git and the crash is gone!
Wondeful result, thank you to ddennedy for fixing that. I look forward to making good use of this program now.