This won't be any help, but I can tell you that I have had really weird problems when programatically setting focus to form controls -- without any page frames involved. It was confirmed as anomalous behavior by a much more experienced VFP developer, so I know I wasn't crazy. I just gave up and worked around it.
"Ignorance more frequently begets confidence than does knowledge."
-- Charles Darwin
"I am invincible! Invincible...OWWWWWWWW!"
-- Homer Simpson