There are numerous other threads in this forum where people have shared that even after booking a single award for themselves they are still unable to book awards for a P2 on future trips. You will also find evidence of that experience in the comments section of several blog posts that tout TK as a great transfer option. The sad part is it seems to be random, which is crazy. Some folks don't have a problem and others do (even under seemingly same circumstances)

Good luck.

Regards