I met the same problem using ActionScript3 and Flash Professional CS5. There are two problems with dynamic TextFields:
- When you set style "Bold" for a text field in CS5, the "bold" property is not available in the TextField object in ActionScript, its defaultTextFormat.bold is alway false; I don't know if we can get this property anywhere else.
- When you change the text of the dynamic TextField object, its style changes to normal no matter whether it was bold previously.
This is really a bug in TextField, Adobe should fix this to implement TextField in an expected way.