I'm assuming that's because of (setq completion-cycle-threshold t).
Apparently, that's because minibuffer-force-complete, called from minibuffer-force-complete-and-exit, somehow interprets it as a repeated invocation.
Maybe it should examine last-command and do something with it, instead of performing the completion-in-region voodoo it's doing now. Or minibuffer-force-complete-and-exit should call a non-cycling version.
Previous by thread: bug#20953: 25.0.50;	with icomplete, completion says "Matched" and then returns something	else.