Hi 
It's a rare and intermittent set of bugs. The precise cause of each
one is unclear and difficult to separate out from all the rest that
cause this. One common factor seems to be having the
"Always create a backup copy"
box ticked.
If you go to
Tools - Options - Load/Save - General
and then untick the box "Always create a backup copy" then the images
should stop vanishing. I'm not sure if it helps with the
sub/superscripts format issue.
It is a good idea to keep a copy of images safely in a folder nearby
in case they do carry on vanishing! Has this been happening only with
files kept on a network?
Note that almost everyone who has "Always create a back-up copy"
ticked will suffer no problems at all. It would probably help us a
bit if you were able to post a bug-report but i'm not sure if this
guide really helps collect enough information in Xp.
https://wiki.documentfoundation.org/QA/BugReport/Debug_Information
to be honest i would have a really tough time trying to follow that
page's advice so i completely understand if you don't.
Regards from
Tom 