From reading the rules it seems that two disks can pin each other with neither doing enough damage to kill each other. Since damage is removed in the end phase the disks will permanently pin each other. Am I understanding correctly?

Yep, you'll have to throw some additional combat at them if you want to end it.

Thanks for quick reply and merry Xmas.

Realized I missed an explanation here that may not have been clear. Pinned disks cannot be activated, but Pinning disks can. So if the player whose disk is on top wants to, they can move their disk off whenever they get the chance.

During the end phase, each player removes all tokens from his disks,
except wound tokens.

Rules page 10. Bottom right paragraph. What vorpal_Cortex quoted.

Wound tokens are not removed, but "Damage" tokens are?

There is a difference.

Yeah, you're right. Only wounds remain. Damage tokens are removed in the End Phase each round.

Wound tokens are the broken shield things, where as damage tokens are the starburst looking things.

for that matter the tokens from command cards, empowerment, and activation, as well as whatever else they come up with are as well.