Can't rebase aircraft

[dumb_user]

I am playing the Poland campaign, difficulty Field Marshal, scenario Bug river. I have 2 fighters, 1 Stuka, 1 He 111 and 1 recon plane. I rebased the first 3 of them from the airfield at Rozan to the captured airfield north of Warsaw. Now I can't rebase the remaining aircraft to that airfield and I also can't rebase those at Warsaw back to Rozan (I don't want to, but even I wanted I couldn't, because the rebase button is grayed out.
The Warsaw airfield isn't a dirt airfield where only 5 planes can be based, and I have only 3 there anyway.
I didn't choose a restriction in the number of allowed rebase actions (if it even exists) on the strenghts and weaknesses screen at the beginning of the campaign.
Is there such a restriction when playing Field Marshal?

Now it is 2 or 3 turns after the post above. Meanwhile I captured another airfield, and now rebasing is possible again.
Still I don't understand why it didn't work before. Does anybody have an idea?