Under normal circumstances, you wouldn't need to restart VA. Are you running any plugins or are you using any profiles that may have ill-behaved commands?
Something you might want to try is redoing your speech profile: http://voiceattack.com/smf/index.php?topic=64.0 (ignore the title).You might also want to scan your system for corrupt or missing files: https://support.microsoft.com/en-us/kb/929833I do this regularly, just to make sure things are still working right.