booting from CMD hd native partitions, Fast Serial

I'm writing a boot block to a CMD HD (using VICE, and it's been tested with a Thunderdrive, using CMD ROM)

The following is testing in Vice:

C128 Bootblocks can autoload additional boot-sectors, meant for use with specialty programs.

What I notice is the following:

- Boot block at $0B00 is loaded from the native partition, Tr1, Sect0

- Additional 3 blocks are loaded to $E000 in bank0

- Bootblock code executes, which starts with an IOinit.

All of the above runs in "Fast Serial" because the C128 kernal routines detect the CMD can do Fast Serial.

Next, I use the Kernal Open routine and expect the 'Fast Serial' flag ($0A1C) be set to $C0 like before.

However, it remains $00 (as was the case since IOinit).

When using  CMDhd with a 1581/1571/1581C/partition this behavior isn't seen.

Has anyone ever run into this issue?

I've dug through the code c128 uses (with help of the mapping128 book) and can't see an issue there.

The best I can say is CMD HD keeps talking 'Fast' but somehow the 'Fast Serial' flag doesn't get set during IEC-Talk.

Are there any fast-serial fans on this forum?