Image / Media Resizing Stopped Working

Recently, the ability to unlock and resize the position of an image, media source, text object, etc., with a mouse has stopped working. As a result, I can no longer use the mouse to easily resize. I *am* able to use the transform edit for this, but that is painful. Does anyone know why this capability would be broken or would just stop working? How to fix? I'm using 31.0.0 64 bit on Windows. Nothing obvious in the log files.
 
So... the "LOCK PREVIEW" was it. But what seems to be a bug is that the lock on the Sources panel was showing the lock OFF, while the menu item that displays on right click showed it as on. Looks like the lock icon in the Sources panel somehow got out of sync or is not working otherwise. Thanks for your help!
 
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