"Carry-over of sound" from previous tune occurs 
It even occurs when manually running Grauw's vgmplay in sequence. It also happens on real hardware - so I believe openmsx 17 emulates this issue correctly.
[Updated: I might have found out why]
I have a vgm-clip (=raw register data) recorded (openmsx vgmrec) from Moon Blaster. The clip is using the drums in the first frame.
Documentation says: "All registers are cleared to 0 by initialization (initial clear IC terminal = 0).", so I do the same before playing a tune (I also do the required waits between writes, 12/84). The problem is: The drum's FIRST sound is OFF/WRONG (a high metallic sound) if another non-drum-tune is played *before* the reset. If I start this clip once again after it was first run (and doing the normal reset), things are audibly correct, no high pitch sound.
How can I possibly reset, if not setting all regs to 0? I know bits and bytes, but I don't really "get" music that well - could it be that some of the registers below is carried over in the first "frame"? Like modulation, vibrato, envelope, attack rate, decay or whatever it is called in the overview below?
(BTW: I am not using FM-BIOS. Have no familiarity with that.)
This is strange :(
--I've made my own tool, and can easily see the commands/content.