Time machine GUI fails when certain folders are selected
I just tried to use the Time Machine GUI for the first time since I upgraded to Yosemite a week or so ago (just applied the OS X 10.10.1 update last night). When I start Time Machine from its icon in the menu bar, with my Downloads folder window frontmost in the Finder, all it shows me in the stacked history windows is just the current contents in the top window -- none of the windows stacked behind the current Downloads folder window is selectable, those windows are not titled, and their red CLOSE buttons are not illuminated). The history markers on the right side of the screen show I have backups back to Dec 2013, when I purchased the iMac 27", and the markers animate when I roll over them, but selecting any of them does nothing. The up/down arrows to the right of the stacked folder windows are not selectable.
If I open my user folder, or have no Finder windows open on the desktop and select Time Machine the same way, the GUI operates just as I would expect it to -- all of the stacked windows are selectable, as are the up/down arrows, and the history markers on the right side of the screen produce the expected behavior when clicked.
Just to check, I drilled down into Backups.backupdb on my TM volume using the Finder, and I can see all the dated history folders and their contents.
Can someone tell me what's going on here? Thanks.