As much as I like Flash Builder 4.5 for PHP, there is one bug in it that I truly hate. I decided to post it here so to save you tons of time trying to figure out what is going on.
The bug is simple. When you have Flash Builder's Network Monitor Enabled, It will simply not stop at the breakpoints on the PHP side of your data classes.
To have FBPHP stop at the Breakpoints of your AMF classes you usually use the Debug as PHP application. It works great, except when your network monitor is enabled. If it stops working, just make sure that the Network Monitor is disabled.