Before you spend too much time on those keyword metas read this: HEAD Tags. It’s a great explanation of all possible head tags. What you don’t find in there is the meta tag for keywords because those are no longer recommended (even by Google).
To your question: The keywords in Front Matter is a list and that has to be enclosed by square brackets like keywords = ["word1", "word2"]. I assume this solves your problem.
I had to delete a comma after {{ if $i }} - and then it worked perfectly - many thanks.
Would do that but usually this breaks something in my templates and thus has to wait until I have some spare time around Christmas …
and sorry for confusion, I actually use v0.18.1 BuildDate: 2016-12-30T11:05:34+01:00 - last year Christmas time for exactly the same reason.