Shift + Left-Mouse Click to select multiple epubs Fails

I wasn't sure where to properly post this, but it's definitely a 'Library Management' issue, so I've posted it right here.

Since I updated Calibre to 4.12.0 a few days ago, I can no longer select multiple epubs for bulk actions, using 'Shift + Left Mouse click. This is a really bad thing and a really big deal. Yikes!

And yes, every other program on my Windows 10 PC still works perfectly when using the 'Shift + Left Mouse click' to select multiple lists of text or files.

And yes I've tried both Shift keys, and two different mice... no change.

It's a singularly Calibre specific issue. Help.

Frizzell