I'm currently running 19.1.3 BUILD 7, and somewhere along the way, this setting was ignored.

I thought this was just a minor bug that would be solved in the next release, but now Ḯ'm updated a couple of times, and it still exists, so I thought I would report it.
All my stills get 50 Seconds when I drag an drop them to the timeline. Not a big thing but it's a couple of extra clicks for every image I add.