Last modified: 2012-04-16 09:15:56 UTC
Preferences -> Apearances -> "Threshold for stub link formatting"
seemingly randomly marks links as class="stub".
For example, set threshold to "5000 B" and visit [[Special:Contributions/Zacky-V]] (edits on 11 February 2011): page "A Skylit Drive" (13+Kb) is even marked differently in different rows.
Did this change recently? That is did you try this before the 1.17 rollout and only now it doesn't work?
No idea; I don't use this option, but 2 other users in ruwiki complained just after the switch to 1.17.
There was a bug just for Special:Contributions Was fixed in r82297 and deployed in r82363.