Not sure if it's relevant but when trying to attach the file I got an error from Jira. Having opened the file in a text editor and saved the error went away. A binary diff shows no difference. Cannot reproduce error on PC.
I've seen this before. IIRC the text comes back if you resize the window, but that's a lousy workaround.
I tried debugging this at one point and ended up going quite deep into the swing code. I suspect there is something funny going on in the Mac platform code that we need to work around, but at the time I couldn't quite get my head around it.