While editing a message, Preview very frequently results in the following error message:
Database error
A database query syntax error has occurred. This may indicate a bug in the software. The last attempted database query was:
(SQL query hidden)
from within function "MediaWikiBagOStuff::_doquery". MySQL returned error "1030: Got error 127 from storage engine (localhost)".
... and then I've lost the edited content (!!!) unless I was careful to CTRL-A CTRL-C to copy it to the clipboard (Windows). Very frustrating!
Clicking on 'Refresh' normally works, even in modern versions of IE, I think. Other browsers I know of have no trouble with just clicking on 'Back'.