Hi,
Forgive me for the somewhat vague bug report; I hope this is enough to pin down the problem. The accept completion for command names seems to have a problem when the disambiguation character is a space. I defined a climacs command com-new-find-file, but am unable to type it at the M-x prompt because there is a com-newline-and-indent; typing N e w SPC does not lead to a space being inserted. Using C-/ lets me click on the New Find File command, so it's definitely there.
Cheers,
Christophe