I went to check out your issue, but im not ready to upgrade to r213 yet...
so im going to guess that there is alot of flashing and flickering at the transition point...
this would be do to the system changing layers 60 times a second while the system makes "one tick" and he is at the >250 position.
I would set the "inside house" theme to a separate layout all together.
you could using the " trigger once while true.." function, but I doubt it will help.
... or, on trigger, set the character about 10 pixels out from the trigger pixel position so he is no longer at that spot.
hope this is useful.