ZDoom

I'll be honest here: This is way too off the beaten path to fix. I have an idea what's causing this but it is code I wouldn't dare touching for an effect that can only be observed by cheating in very specific situations.

I was fooling around with Heretic voodoo dolls in recently released Unbeliever Heretic megawad and I stubled upon this bug:

1. Run Heretic (no mods).
2. Go to E4M1.
3. >kill monsters, so they wouldn't bother you.
4. >give all and activate Tome of Power.
5. Go to red crusher with Crossbow in front of you.
6. Let yourself crushed to death, but start and keep firing before you die. This is critical, the bug won't occur if you don't fire.
7. >resurrect
8. You will now have permanent Tome of Power. It will go away if you change weapon, however.

The same will happen if you get killed by lava or monsters.