SR MBP 2.2 (128VRAM) display blotching in logon screen only

[amusiccale]

I have a June 2007 MBP, base model running Leopard; At the logon screen, the default space background appears to have a fairly large magenta blotch in the nebula portion (looks like it's running a lower color resolution here), but when I log in to my default account, it looks fine. In my guest account, however, it persists. Any ideas? I don't have applecare (out of warranty), but I do have the extra year through the mastercard. Is this normal behavior?

(I tried taking a screen shot --I don't have a camera at the moment--but it looks fine when it's back on the default account)

 

[amusiccale]

Ok--I went in, changed the resolution, changed it back to 1440x900 and then it returned to the correct color depth. I'd like any ideas as to how this happened--it seems to be fixed at the moment, but I'd like to know if this is the start of something permanent. People with 2.2s that went out: Is this how things began?