I got my 46a650 Late january (2009), and I have the same problem. Normally, the tv turns off fine, but when there is no signal on hdmi, and I turn off the tv, it seems to happen. As long as I turn off the tv within reasonable amount of time, after i turn off my ps3 for example, it is fine. Another workaround is if you change the signal source (for example from HDMI1 to TV) before turning it off, it seems fine.

It is annoying, yes, but I decided keep it. My first 46a650 had different kind problem with hdmi, and I really don't wanna go through another replacement process.