Can confirm regarding the impossibility to launch after having reverted to the VAB (due to me crashing the previous vehicle, for example).
I get back to the VAB, do my modifications, and when I press launch again, nothing happens. I usually have to restart the game, or go to the main menu, in order to fix it.
[EDIT]
As a small update, I can say that sometimes, if I wait it out a few minutes in the VAB, I suddenly become able to relaunch the vehicle again... very odd.