Paragraph Style Weirdness

I don't know if this is one issue or two or three separate issues. Let's assume they're related. It may be user error on my part -- that's entirely possible. But it isn't how I would expect InDesign to work.

At present, my Normal paragraph style is defined as using 12pt Constantia. That's what the dialog box says it is, and that's how the document appears. But if I click in a paragraph, the Paragraph Styles list shows Normal+. If I then Alt-click to apply the default Normal style, the paragraph turns into 16pt Libre Baskerville!

If I then manually switch the paragraph back to 12pt Constantia using the toolbar at the top, the last line of the paragraph has extra leading above it. Not below -- above. That is, there is now extra leading _within_ the paragraph. (See screenshot below -- one paragraph in each column exhibits the problem.)

At present I've defined a Paragraph Style (derived from Normal) called Chapter First Graf. Within that, under Drop Caps & Nested Styles, I have chosen a character style called Drop Cap Character as the style for the drop cap. Or at least I _think_ it's for the drop cap. And of course, the character style Drop Cap Character is 16pt Libre Baskervile.

What appears to be happening is that InDesign is applying the Drop Cap Character style not only to the Chapter First Graf style, but to all of Normal, overriding the settings for Normal. This may be the source of the user error. I was thinking that the setting in the Drop Caps & Nested Styles pane would apply only to the drop cap. Because why would it need to exist if it's going to apply to the whole style? In any event, it's certainly propagating clear back up the object tree to Normal.

Attaching a couple of screen grabs so as to show what I'm talking about. Help would be much appreciated!