It's a bug with the inventory system. Using one item on another item crashes the game, and sometimes clicking randomly in the inventory crashes it. I am working on the problem, but it shouldn't actually hold you back from playing the game all the way through. All the puzzles in the game can be solved by using the inventory items in the outside world, and all items that need to be combined can be done so outside the inventory (for example, when you get a container and want to put something in it, use the container from your inventory on the item in the outside world). Once an inventory item is in your possession, you can't use it on another item in your inventory, but the player will simply discard the old one and put a new one in the container if you click it in-world).
Also, you can switch cursor modes between EXAMINE, INTERACT, and WALK TO simply by right-clicking... no need to use the inventory menu for that (and there's no way to select WALK from the menu).
Good luck! There's a lot more to find and a deep mystery to unravel... and two endings! Neither of which you shouldn't be able to reach given the current bug. Just make sure you save often (which is always good advice in an adventure game anyway), because sometimes any click in the inventory can make it crash. I was able to play it all the way through several times with no crashing at all, and one time in one of the more tense scenes I accidentally missed the item I was reaching for and crashed it.
...now that I said that... I think I've realized what the problem is. Wish me luck, and good luck to you on your investigation!