ToME WikiKhymChanur: Currently, if you're in a vault and have the Probability Travel effect, if you move into a wall you'll pop right out of the vault. This can be very handy for a quicky and easy escape from a vault, for either when the level prohibits the up/down level functionality of prob-travel, or when you want to escape the vault, heal up, and go back in for anohter try. However, if you frequently use prob-travel for non-vault purposes, a simple typo while in a vault will pop you outside the vault, meaning you have to make your way back inside, and whatever situation you might have set up might have changed; additionally, the "quick escape from vaults" aspect of prob-travel is a side effect of how the code prevents you from using prob-travel to get inside vaults.
I can see two ways of changing this. One would be to simply prohibit the through-the-walls facet of prob-travel while inside a vault. A more complicated method would be to only disallow through-the-walls prob-travel if you bump into a non-tunnleable vault wall. This would allow the use of prob-travel to get past the diggable walls of vaults without actually digging them, while making it so that bumping into the non-diggable outside wall of a vault won't do anything, rather than take you to the opposite side of the vault.
JaekTheBarbarian: Why not leave it the same way and have a "Teleport (y/n)" sort of warning (as with random teleportation)? Or perhaps "Jump (y/n)?"