It used to be that the number of contributions displayed on [[Special:Contributions]]
by default was determined by preferences (like [[Special:Recentchanges]] is), but
recently the default number is always 50. This change appears to have been introduced
with r21664 (then removed in r21666 and reinstated in r21667), where a hardcoded 50
is now used. It's quite possible that the former behaviour was accidental, but it was
quite useful; is there a good reason for a hardcoded limit now, or can that specific
part of the revision be reverted (it was only a small part of a large change)?