@CybeX
Well, the debugger shows a as "<not accessible>", so unless its value has been optimized out that seems to be the cause of the SEGV. I admit I don't know how/why, assuming you only put items into fileInfoImageList via the code you show.
I would start by just checking you can visit/print out all the QFileInfos in your lists before you start the std::sort()?
I would also force a complete rebuild just to make sure. The placement of the debug breakpoint on line #319 which is blank looks odd to me, it's not supposed to do that....