Not sure if this has been mentioned before, but you can find a hidden inventory slot. It is located to the right of farthest right slot second from the top. You have to click juuuuust past the regular slot but you can place an item so that it looks like it's falling off the inventory window. I'm at work at the moment so I can't upload a pic, but it's really easy to reproduce and can be done with every character I've created. Let me know if a pic would be helpful.
Just posting to confirm that this works for the second, third, fourth, and fifth spaces down along the right on the inventory.
I vote this bug to *NOT* be fixed and be a Very Special Secret shared on these forums for the die-hard fans of Dredmor who come here to share their leetness. I does my ego well to have such a hidden usefulness that only me and a few Dredmor-neophytes know about. Maybe there can be T-shirts "I have SEEN the hidden inventory"... I can see it now... the world is our oyster .../Funnily enough I still am kinda serious here EDIT: for some reason burnt out my wand of bling fiddling with it... it dropped to the floor burnt out... couldn't reproduce with other wands. But yeah it works, all rows the last spot except the last row. It's tricky to do but the items are retrievable and save fine.
Hah, that's funny, I never bothered checking the other rows. I tried it on the other side of the inventory but not down the right side! EDIT: I haz an avatar!
This isn't an extra inventory space. It's a pixel-wide expression of the first inventory space of the next row. You can't put an item in the "extra" space if there's something already occupying the first space in the next row, you can't put anything in the first space of the next row down if there's something in the "extra" space, and you can't put anything in the "extra" space of row 6 at all because nothing comes after it. It's weird but functionally useless.
Meh if that's true then go ahead and fix it *Dashes all hopes of world domination and desperately tries to cancel his order of 1000 T-shirts with "I have SEEN the hidden inventory" inprinted on them*