I'm guessing that you have a communications problem sending stuff to the DSP4000, and it is losing or corrupting characters. This would explain all that you are seeing.
The DSP4000 is a 25 year old design, and is nowhere near as fast as a modern computer (it has an 8MHz processor, rather than 2-3000MHz), so you may just be sending stuff faster than it can handle it.
I don't really have a solution, unless you can find a MIDI interface that is slower, or can be "throttled." I am, alas, unaware of such a thing.
