At the moment, revealing a dropdown menu in inline editing mode requires two clicks - BUT if you double click too fast, the table flips to form editing mode and the form pane jumps in from the right. This is annoying when you're trying to work fast (at least to me!). Would suggest controlling the toggle between inline and form editing modes ONLY in the buttons at the top, so users wanting inline editing can double click at any speed. Users who prefer form editing can lock that in with one click on the top bar.
One further thought on that - when the form pane is triggered, it doesn't default to the field you're trying to change in the inline edit - at least on my forms which have several tabs on them. So the appearance of the form is quite unhelpful.