I am unable to reliably send/receive tagged VLAN 1 frames on a RB1100AHx4 (aka RB1100Dx4).

The default switch port configuration is default-vlan-id=1 on all ports:
I set up a normal VLAN interface like so:
As expected, VLAN 1 frames are sent on ether2 untagged, and untagged frames received are received in VLAN 1.

However I want VLAN 1 frames to be tagged on ether2 (just like every other RouterOS device). You'd think this would be just:
This does not work. I've tried many values for default-vlan-id other than 0 with the same result. VLAN 1 frames are sent untagged regardless.

I've tried setting "default-vlan-id=0" for all ports plus the switch-cpu ports. Occasionally this works, but not always. Annoyingly, after a reboot the problem recurs, and another change to a different default-vlan-id on all ports sometimes works (but not always). It looks like when the switch chips are reprogrammed it starts working, but you need to make switch config changes to make that happen.

RouterOS tells me the switch port vlan-header=add-if-missing feature is not supported on this platform.

I've tried with RouterOS 6.38.something, 6.39.3 and 6.41 -- all had similar behavour.

Is there something I'm missing? Is this a bug, or a limitation, or a feature? How do I send tagged VLAN 1 frames on an RB1100AHx4?

This is a known issue on the RB1100AHx4, confirmed by MikroTik support:

This is a know issue, we are working on fixing it, but sadly for now you will have
to avoid using VLAN interfaces with VLAN 1.