There seem to be A LOT of bugs and slow speed issues in the current batch of CC programmes especially Photoshop and InDesign. Adobe, please hold off releasing these things until they are thoroughly tested.
Are you being serious?
Please check the Channels Panel.
If you perform a Layer operation Photoshop has to switch to the composite Channels.
Err, yes, I am being serious. I have never found this before, otherwise I wouldn't have posted the problem here. Thanks for your 'kind' words!
Perhaps a bug was fixed in CC. You wrote that you used "Q" to enter quick mask mode for the background layer. Quick Mask mode should not be an available option for the background layer for the background layer does not support transparency and can not be masked.
However it look like Photoshop allows you to enter quick mask mode even when there is only a background layer, If you then change the background layer to a normal layer and use the gradient tool though the quick mask icon in the tool bar indicates your in quick mask mode when you use the gradient you wind up painting on the converted and targeted layer. I tested CS2 CS5 CS6 perpetual and CS6 subscription and CC all seem to work the same way the converted targeted layer get painted on.
Converting the background layer seems to target that layer but not reset the quick mask icon in the tool palette. Click the quick mask icon twice after converting the background layer will solve your problem. I feel the real problem is that Photoshop allows you to enter quick mask mode on a background layer. It should not be an option for background layers can not be masked.
Quick mask mode though can be useful for making selection on a background but the newer versions of Photoshop have the quick selection tool.
I have never found this before
This is no bug.
If you perform an operation that affects the Composite Channels naturally those have to become selected in the Channels Panel and the Quick Mask Channel is deselected but still there.
Same as it was in CS6, CS5, …
Edit: Reselecting the Quick Mask Chennel via the proper Keyboard Shortcut seems to work fine.
Also you should be aware that this is a user to user Forum, so you are not really addressing Adobe here, even though some Adobe employees thankfully have been dropping by.
GrizzlyHippo, in which exact version of Photoshop was this behaviour different?