Last modified: 2013-04-06 14:48:05 UTC
The tools using "mw-js-message" break the UI: while all the other contents move when the "mw-js-message" div contains something occupying space, the sidebar (quickbar) remains in the same position, overlapping the blue top part of the skin. May be "mw-js-message" div could be placed into (or alongside) the "siteNotice" div instead, so that it would appear under the blue top bar? P.S.: all of this is observed on English Wikipedia since June 22, 2012; though the problem probably existed before that date.
*** This bug has been confirmed by popular vote. ***
Assuming you meant messages created using mw.util.jsMessage: this has been (retroactively) replaced by the new mw.notify API, which has no such problems. If you meant something else, do tell, preferably with screenshots or example code :) Closing as invalid for now.