I believe these should now be working again. I have absolutely no idea when or why they stopped working - so I can only assume that something I touched in one place broke something in another - which isn't ideal!
I thought that it was to do with the date alignment that I fixed a couple of days ago, but I can't see how. The popup 'engine' itself was causing an error in Remix which fortunately didn't impact the saving or creating of entries, but didn't obviously give you any feedback about whether the save had worked or not.
Let me know how you all get on. You may need to do a full reload on your browser, but I suspect that by now the cache expiry should have passed.