When switching between, for example the soldiers menu and the dropship, it often jumps unintended between Bases. So I have always an close look that I am moving my soldiers still in the Base where I wanted to. But I can not exactly figure out when specific, or at least I cant while I am writing here. I will have a look on this when playing.
Regarding the unintended jumping between bases.
Was just in preperation for an assault on an alien base. Base "UDSSR" was selected to adjust my crew. I clicked on the soldiers tab and the base switched to the Base "Latin America".