Some time since starting to use 6.0rc (i'm not sure at which rc version it started or if it was present since the first one, as i've just noticed it) the manual tx power table stopped working.

Frequency Mode is still set to "manual txpower", like it was since day one. If i set Tx Power Mode to "manual", Current Tx Power lists default power settings (which is nearly max. for most of the rates). If i set it to "card rates" and set the Tx Power field to some value, Current Tx Power lists maximum values again.

About the only Tx Power Mode setting that works is "all rates fixed".

Am i doing something wrong or is this feature currently broken in 6.0?

ROS 5.22 is the same behavior

For RB2011 and RB951-2n you can use only tx-power-mode=all-rates-fixed or use the frequency-mode regulatory-domain for lowering the tx-power signal, due to limitations of the chipset.

Then if the developers knew this limitation of the chipset, why not remove this option from the command set and winbox to stop you trying to set it? Is this limitation documented in the wiki? I can't see it anywhere.

Agreed. Some mention of it in the documentation or disabling it in winbox, term and webfig would've been a good idea.

I thought it was a 6.0 issue because i've installed it about the same time i've switched from a previous RouterBOARD (on which manual-tx-powers worked) and never checked till today.

I agree. If you cannot perform a function due to chipset - disable the function and document it.

We have enough real issues to chase without having to chase unknown chipset limitations.