It‘s not a bug, it‘s a feature. Please see discussions in #2844 and related tickets.

No, it is a bug. I have permanent immunity after entering a door, please see the latest nightly and related literally in your face bug.

Permanent immunity should indeed not be, Tux should only be invincible during the fade in effect.

I can reproduce this, and think I understand the mechanism for this: #3051 repurposed the variable m_is_intentionally_safe to control invincibility, instead of creating a new one; before the PR the variable was only being read by Player::draw to control a "blinking" effect during the post-damage safe period, but had no effect on the game logic; the variable was set to true by Player::make_temporarily_safe, which may get called on spawn or teleport under certain conditions, and set to false in Player::kill.

I can reproduce this, and think I understand the mechanism for this: #3051 repurposed the variable m_is_intentionally_safe to control invincibility, instead of creating a new one; before the PR the variable was only being read by Player::draw to control a "blinking" effect during the post-damage safe period, but had no effect on the game logic; the variable was set to true by Player::make_temporarily_safe, which may get called on spawn or teleport under certain conditions, and set to false in Player::kill.

That is correct. I should have chosen a diffent name for the variable, it is obviously misleading.

I have split the flags according to their intention and renamed the flag that avoids the blinking effect to make it hopefully less misleading. I did some tests with the door and the scripting function and did not see any unintended behavior, but please give it a try and check for yourself.