Comment 39 for bug 927515

Yes it is imap to imap, but actually that doesn't seem to matter, the problem occurs before the move is initiated. I now have a slightly different ways of recreating it, and perhaps more useful.

Select multiple emails over more than one page so that there is a need to scroll.
wait until all emails are shown selected.
click on scroll bar to move to another view of the selected documents.
the system goes hyper!

Another is to click on the delete button instead of trying to move the scroll bar.

Bottom line is that operations (not apparently all operations) that involve multiple selections can kick off some very intensive cpu activity that can go on for several minutes. It doesn't happen every time, but does seem to have something to do with the status of the folder in which the emails are being selected - so maybe something like re-indexing the whole folder, or compressing it on the fly, or something like that. However there is no apparent disk activity, it's pure cpu although the memory footprint does change up and down a bit.

Hope this helps.