Flash CS5 MAC input textfield problem

Question

I'm developing external Flash Panel with Flex Builder 3 which can be opened through Window > Other Panels. While using that panel it opens more .swf windows as popup dialogs. Some of those windows contain input textfields. Those textfields have some character restrictions. The problem is that when viewing those popups only in MAC and only in Flash CS5 strange problem occurs:

You can not enter more than 1 symbol of letter "a" or "A". Id does not matter which popup dialog I open or which text field I use. As soon as you enter letter "a" or "A" in any of the textfields it does not allow to enter more.

Any ideas where to look for the solution?

Thank you