I finally had some time to experiment and sent a fleet out into space and stop. Then using the view TF option sent a second fleet out with orders to absorb the first fleet. When they got there I did not get the expected error messages, but when I looked at the TF screen the remaining fleet was empty of ships, vanished into thin space. I was able to get around this by using the similar join command and keep the ships from vaporizing, so this is more a word of warning. Watch out for the abosrb/self destruct command, or the, oops, another fumble fingered helmsmen explaination.