MIDI File won't play in WF11, will in Acid Pro 10 and Windows Media Player|?

[SuitcaseOfLizards]

And the voyage of discovery continues...

Waveform 11, latest build, Windows 10 PC, Realtek audio.

I have a pack of MIDI bass loops from Producerloops. All loops play in Acid Pro 10. All loops play in bloody Windows Media Player.

But 21 of those loops WON'T EVEN LOAD IN WAVEFORM 11.

Clicking on it won't load it. Drag and drop from Explorer onto a track won't load it. A quick look with a binary editor doesn't show anything that doesn't look kosher to me (but I'm no expert).

Any ideas about what might be happening? Or should I report this as a bug somewhere and attach a few of the offending MIDI files?

All help appreciated!