Rob, thanks for your comprehensive and thoughtful reply.
... bug 31676 (the 32-stylesheet limit of IE, https://bugzilla.wikimedia.org/show_bug.cgi?id=31676) which IMHO is a very serious time-bomb waiting to explode. I hope it makes it into "1.19wmf deployment" as planned.
Is this all versions of IE?
Yes indeed.
The addHandler() function in JavaScript does not seem to work inIE8 anymore. We worked around this by using jQuery's "bind" function.
Is there a bug for this problem?
I haven't had time to produce a minimal test case to show that it happens, just a huge blob of code, so I haven't filed a bug report. I did mention it in this list and got the advice to use ready() (sorry, I wrote "bind" above):
http://lists.wikimedia.org/pipermail/wikitech-l/2011-December/057166.html
DanB