So, I was on Cambion Drift. I went to pick-up a tranquilized conservation target. I was in Operator mode. I picked it up, but before the pick-up animation could finish and before the animal tag was rewarded, I transferenced back to my Necramech.
After that the next time I left the Necramech, I could neither enter it nor assume Operator mode - I was stuck in Warframe mode.
This was a wee bit problematic since I didn't have proper gear with me aside of that Necra. Eventually found a work-around - I sought for another animal to capture, and after that, I could get back to the Necramech.
Screencap of the situation, the conservation target is just hanging there with the pick-up drone under my aim rectangle. The pick-up refused to finish.