There's two different (but very possibly related) bugs occurring here.
I think that the OP is refering to two dretches on a wall touching each other, which causes the views to go spinning wildly. This bug happens to everyone and seems to occur on every server and client.
I think that Lava and David are refering to the bug where the orientation for one player suddenly goes incorrect in a more methodical, less-spinny way when on the edges between surfaces (try it on the lights on ATCS, where Lava first reported it). This bug occurs across game.qvms, but only happens to some users (across client executables) while never affecting others. Those affected see the occurance in demos and while following other players, while those unaffected do not.
Both bugs are in places in the code that aren't the easiest to figure out, but the later is particularly challenging because I for one cannot reproduce it whatsoever.
[edit] grammar fix