Hi
Why you don't write this to whitebream and ask for help?
whitebream wrote for the RC5 VHDL Core on his page:
"The project that this core was designed for is cancelled before any hardware was available. Therefore this decoder has never been tested on real hardware. When you implement this core please provide feedback on any changes that are needed to get it working or just bugs and comments in general."
I downloaded this core and I'll view it's code for my own interesting in next days. If I found any hints I'll let you know this.
Greetings
Jens