I dinnae see's whut all tha trouble be's aboot! Thar be's two kinds O characters ... Dwarfs and ... others.
It is not just a dwarf thing it is a toee thing. I can confirm there is no tumbling in medium or heavy armor.
According to the description of the Tumble skill in the original ToEE booklet, on page 75: "The Tumble skill check is automatically rolled when: ... The mover is not wearing medium or heavy armor (does not apply to dwarves)." I take this to mean that dwarves are supposed to be the only race that can tumble while wearing medium or heavy armor. However, this has never worked in the game. My impression is that it is something that didn't get implemented correctly in the game engine when it was released and that the Co8 modders were unable to fix it.
You can’t use this skill if your speed has been reduced by armor, excess equipment, or loot. You can land softly when you fall or tumble past opponents. You can also tumble to entertain an audience (as though using the Perform skill). The way I see it is you can't tumble if something is restricting your ability to move freely, or you are carrying a heavy weight. Basically, anything that removes your dex bonus would also prevent you from tumbling. Just my opinion mind you.
Dwarves. Drinking.. Dwarves... Tumbling.... Dwarves..... Drinking...... Dwarves...... Tossing......... Is ther a pattrn ere or *BELCH* hansd on i ned anthr beerrrr *ERRPPPP* !