What's the difference between the "Tags" column and the "MyTags" column in the Library window?
They show the same data (i.e., tags that I've added), but the Tags column doesn't sort correctly. I think it's broken.
Here's my library sorted by title:

Here's my library sorted by MyTags:

AND NOW, here's my library sorted by Tags:

What?! It's not sorted by the values in the Tags column, even
though the sort arrow in the header bar indicates that it should be. It's actually sorted by title, but it's not respecting the changes to the book names I gave to the MacArthur commentaries (it's using the built-in names). What's up with that?
Clicking on the Title column again gives me back the correct Title sort again.
So what is the Tags column for? and why does it act the way it does?