I think Disgaea had a similar concept of items having dungeons inside them.
Now off to break the game!
EDIT:

Game "froze" with menu still available, as per usual when it breaks. Screenshot function still works so that's good. Eating a polymorph potion didn't solve it like it did that one time. The red on the minimap is a monster portal. My guess is the spawning did it, did you check that the not enchanting items with xp runes bug is still fixed with a: monster portals and b: portal runes.
Loading put me at the overworld with all my items, except my armour got cursed. What causes armour to be cursed? It might be unrelated to the bug.
Thrown runes get stuck in place against the healthstone and grindstone.
Entering the item portal I had from before the freeze and load froze the game. Loading after this gave be a black screen and empty minimap. Actions and portal rune use disabled. More loads don't help.
Either I have some crazy luck, or the portal enchantment is always light 2.
I made an item with level 20 light and the portal seems to have eaten it as it's nowhere to be found.
Loading after dying in an item portal dungeon froze the game and the menu. (Sounds still going.)
Probably going to stop for now. The menu magically unfroze, but the game is stuck in black screen land.
Used a portal rune on a fedora with level 20 light. Item didn't get eaten this time. I now have a fedora with level 20 light and level 2 light. They don't stack.
You're jealous:

(Had to do this one manually becasue it's a shot of the menu, but it's not a problem.)