how to import .htmlz files to Calibre?

[mlevin77]

I'm using Calibre on a Mac. I have a bunch of .htmlz files and I can't figure out how to import them to Calibre. I know I can change their filename to .zip and then unzip them to reveal a .html file (and other stuff inside) that I can read. But when I try to import directly to Calibre, here's what happens:

1) it successfully creates a new entry in my Calibre library (with cover image etc.).

2) but when I double-click on it, instead of just opening the text like it does for all other ebooks, it says "Books with the same title already exist. Add them anyway?" and if I say yes, creates another line in the book list. If I double-click that, the process repeats, ad-infinitum. So instead of showing me the contents, it keeps re-adding it to the library when I double-click. What am I missing - how do I get Calibre to have access to the contents?