Was this a file converted over from a .fp7 file?
I've seen and reported similar behavior when editing the text portion of a button--but it only happens with buttons that came over to fmp12 via conversion from an older file format.
Yes, the file I am working with WAS converted from .FP7, but I fired up a brand-new file from scratch with FMPA 12, and it exhibited the exact same behavior. The text fields resize themselves at the slightest provocation. (Changing the fill background doesn't set them off, but almost every other kind of formatting change DOES.)
In your first post you say "selected labels" and here you say "fields". I hate to quibble over details, but they're important when nailing down possible bug behavior. Which have you encountered here?
On windows, using a file created in FMP12, I don't see label text changing size unless the style change requires an increase in width. Italics, bold, a different font all caused a small increase in size. Changing the text color, or specifying an underline style did not.
And when I test this in Filemaker 11, I see identical changes.
You are correct. I should have said text OBJECTS, not text FIELDS. (The text objects started their lives as field labels, tho I changed about half of them.)
I'm using a Macintosh, so it's possible it behaves differently than the Windows version.