When I've written a math formula, whether it be inserted into the main text
or as a numbered equation, the text size becomes huge with the formula
usually disappearing off the end of the screen. If you then reselect the
formula, as if to edit it, it then shrinks back to normal size. I am doing
something obviously wrong?
Looks like a problem with instant preview - but I don't know how
to fix that. Take a look at "Tools->Preferences->Screen Fonts", see if
there are any strange sizes or zoom factors.
I assume this does not affect output, i.e. your PDFs or printouts are fine?