Photoshop can't affect the keyboard - Photoshop doesn't know anything about your keyboard, or the driver for your keyboard.
Photoshop just gets key events from the OS (which gets them from the driver).
So I had assumed. The fact is however, that the problem only occurs when using Photoshop CC, and it just happened three times within five minutes of starting work in Photoshop after reboots. I can work for hours in any other program and not get an occurrence. Interestingly I am having no problem with CC 2014.
The only thing I can think of is that there is a system instability that is somehow triggered by the resource use of Photoshop. The only thing that has changed is that my system drive has exceeded 90% of capacity. That does tend to make things dicey. I'll clean it up and see if things improve. Thanks for your answer.
Do you have any utilities that modify keyboard behavior based on the current application? (Logitech had some of those a while back, and they caused all sorts of confusing problems)
None that I know of. To be fair this behavior has only begun to occur; I used PS CC regularly without problem. The only thing that I can think of is that I recently installed CC 2014, which caused some complexities using Bridge, which has changed my workflow slightly. Bridge CC is a bit confused as to where its loyalties lie. I used to open in ACR and then open from there into PSCC. That no longer works, as it apparently tries to launch into CC 2014 even if CC is open. "Open in" in the context menu does not contain an option for CC, so what I have to do is to launch CC, then go to Bridge and choose simply "Open", which launches an instance of ACR that connects to CC when I choose "Open".
Perhaps this causes some state in the system that, combined by some as yet unidentified keyboard command, causes the keyboard driver to hang. Just a completely uneducated speculation. Using CC 2014 I use my normal workflow faultlessly, so I will just go ahead and get all my plugs installed and drop CC completely.