Take a JU-88 with 4 x 500k bombs and 20 x 50k bombs. The 4 x 500k bombs default to be the first group of bombs to be dropped. Select the second set of bombs (20 x 50k bombs) to be the first group of bombs to be dropped. Jump to a gunner position, then return to the pilot's position. The bomb selector now shows the 4 x 500k bombs (the default group) to be selected without you having touched the bomb selector.
This becomes a problem if you have decided to drop the smaller bombs first with a short bomb release delay. If you are on the bomb sight preparing to drop, jump to a gun position to defend yourself and then jump back to the bomb sight to release the bombs. In my case, I released the large bombs with a 0.05 second delay instead of a 0.30 second delay (my standard for the largwer bombs). The resulting hit attern did not straddle the target as I had planned.
Since, writing this report early this morning, I have verified that this problem is not unique to JU-88. It appears that any airplane that has at least one gunner position and a mixed bomb or bomb/rocket load has this problem. I have found it on the A-20, IL-2, SBD and Val.