Probably not - but someone might.

But you're assuming it's a software problem; yet you say it works with one physical connection (via the PC), while not with a different physical connection - to me, that very much suggests a hardware problem.

The MIDI specification is very specific about what should & should not be grounded - and that is precisely the area in which PC implementations are notoriously non-compliant.
Therefore gounding is the first place I'd look - either your interface is relying upon the PC grounding something that it shouldn't, or it's relying on it not grounding something that it should.

As Per says, if you're serious about this stuff, then you really do need to get a scope and learn how to use it!