Trouble With Door Commands (i.e. Shift+E+2)

There are times when hitting Shift+E+2, for example, will open other available doors on a given aircraft. Then, without changing anything, hitting the same combination on the same aircraft will do nothing more than open and close the main door over and over. I swear I'm hitting the keys exactly the same as when it works! Anyone else have this problem? According to my assignments, Shift+E should only set me up to select a door but it always opens the main door even without hitting an additional number. Anyone find a solution to this? Now that I have Bremen, it would be nice to open doors that are now served by airstairs and service vehicles.