Possible Midi bug in 5.1.1

Since installing 5.1.1 I regularly experience a sudden rush of Midi data when running a project that triggers an external V-Drum unit.

If I start playback from the beginning of a project, everything seems OK, but starting somewhere further in to a project often causes a whole load of drum beats to sound almost simultaneously for about one second then the track settles down and plays in sync.

‘‘Use System Timestamp for ‘Windows Midi’ Inputs’’ is checked.

I’ve tried to reinstall 5.1.0, but the install procedure doesn’t get very far and just closes after a couple of seconds.

Could this be a bug?