I have my Kmail folders listed in “Manually, by Drag And Drop” order rather than alphabetically (right-click on the “Name” bar). However individual folders sometimes go to the bottom of the list for no apparent reason, though it may be associated with changing the sort-order of a message list. Clicking on an out-of-order folder may (or may not) cause it to return where it belongs, but it can normally be moved back manually.
The problem only occurs with top-level folders, sub-folders don’t seem to be affected.
This behaviour is intensely annoying! Has anyone else experienced it?