That's great that you're enjoying it! I'll check the reported bugs. Regarding the inventory items, that's how it is; if you leave the level, they return to their original places. This is because otherwise, the player would have too much trouble constantly going back and forth to recover HP. The doors and stairs, however, once opened or placed, remain throughout the game (unless you use a password).
This theme only allows you to play the mansion level and the race track level. Thank you for the feedback!