I just tried setting salvo to 0 off and on line. It did not change it and used the setting I had it set to before I changed it to 0.
I know salvo 0 used to work because previously, when I had accidently opened the doors, either with troops or with bombs, I would immediately shut the doors and set salvo to 0 to prevent further premature drops, then cycle the doors to clear my error.
It does say salvo 0 is a valid setting also, the range is 0 to 100. I'm going to check the 'Bug' post and if it is not listed, post it as a bug.
fuzeman