I imported an xml file from Finale. I copied material from it into a template I had set up, with no key signatures.
On the Clarinet and Bass Clarinet the score shows, however, a key signature with 2 flats. The notes are all correct, the key signature does not show in the parts (which is of course as it should be, having been transposed to C). But no matter what I do (selecting the key signature + Shift-K - enter “open” or “atonal”), I can not get rid of it. Any ideas how to? and/or why this happens?
Have you tried to copy-paste into a new staff, which is defined as open (Shift K, “open”, alt+enter) ? Maybe it could ease Dorico to do its magic 
aha! thanks! I wasn’t aware that you had to type Alt+Enter after “open” (that immediately works on the staves I mentiond) I just hit Enter by itself … (not really an obvious sequence of key strokes, is it now …)
When you press alt+enter after a key signature or a meter (4/4 or 6/8) it means it only applies to that staff. Very useful, I think ! I am glad it solved your problem — which I did not imagine !