Hmm, interesting. For me, after I made that post, I have yet to notice the same freezing 'return' - there is still a barely noticeable delay in the time update (only easy to notice when like 15 minutes have passed, so that the numbers are significantly different), but it's way less than a second, and I'm not even sure if it's the freezing or just the DateTime widget (either way, I have yet to manage to touch the lock slider on the lockscreen, after pressing the power key, and have it not respond/move - and believe me I've tried to hold one finger right where the lock slider is, and moving it immediately after pressing the power key), where-as on an N900 that doesn't have qtlockscreen entered anywhere in that file, the 'freeze' is ~3 seconds, and the lock slider is indeed non-responsive (I have the fortune of having multiple N900s to compare things on at the same time, thanks to having the misfortune of having two, so far, succumb to the "telephony functions disabled" error).

But you might still be right - it's possible, for instance, the N900 swaps out desktop-classified programs after some long period of inactivity, or something, but doesn't touch the sysutils-classified ones, or something like that. I'm going to report back if/when I see the QtLockscreen start freezing again. (I concede it's possible I don't notice because my QtLockscreen config is fairly simple - no music player/album art/weather/etc.