A number of Mac user have reported this, and it seems always to be some other program or a system setting hijacking the key.
I read up on it, sick of dealing with this myself. apparently adobe apps use an outdated method of polling modifier keys, it was superseded before 2005. Of course, this is only as reputable as a forum opst can be, but I'm so sick of this issue- an issue that i don't encounter in ANY other app on my system.
"Thanks for the link, Sapporo. The info in the link would imply that the Adobe suite uses GetKeys() for keyboard constraints"
"Ten years ago it required polling GetKeys(). Now that just wastes CPU (notice that Photoshop/Illustrator eat 100% CPU while you're dragging any tool.)
The NSEvent mechanism allows you to see the current state of modifier keys without polling, so GetKeys is definitely no longer required."