CSV import not working

I'm trying to use the CSV import and it's not working properly.

I've tried using both commas and semicolons for the delimiters, to no avail.

I've tried keeping the line breaks for new records and replacing them with delimiters.

I've double-checked my list:

no headers
email,firstname,lastname
no extraneous characters

I'm a fairly experienced user, but I'm stumped.

It either imports only the first record, or only the first record and the last record.

Sadly, I've been fussing with this for half an hour. I could have typed them all in by now, but I'm a stickler for getting things to work the way they're supposed to.