There has been a slow and highly confusing set of reports about switching tabs of the preferences failing, apparently limited to certain versions of IE (at least IE8).
Possibly the following changeset is to blame:
https://gerrit.wikimedia.org/r/#/c/4950/
Version: 1.20.x
Severity: normal
Platform: PC
Whiteboard: aklapper-moreinfo
URL: https://en.wikipedia.org/wiki/Wikipedia:Village_pump_(technical)#.22My_preferences.22_tabs_not_working
from https://gist.github.com/1599740
Note that IE8 running in IE7 compatibility mode reports true for 'onhashchange' in window,
even though the event isn't supported, so also test document.documentMode.
https://github.com/yearofmoo/MooTools-onhashchange.js/blob/master/onhashchange.js
has some talk about IE6 and IE7 issues with setting window.location.hash
Since we changed methodology on that as well, might be worth looking into.
Unfortunately closing this report as no further information has been provided.
Derk-Jan: Please feel free to reopen this report if you can provide the information asked for and if this still happens. Thanks!