Mountain King for 2600 played in 7800

At a flea market, I just found out the Atari 7800 plays games made made
for the 2600. Only the Pause button may be incompatible with some games.

I was curious as to what would happen when the Mountain King
(CBS Electronics) made for 2600, is played on a 7800.
Well, everything looks the same until you get up to the hidden world.
It seems impossible to create ladders to climb higher. Both the paddles
and Sega Genesis controllers don't add ladders anywhere as they do when
the game is played on the 2600. And the Atari 'Video Touch Pad',
Keyboard Controller and Colecovision don't remove ladders like the do in
the 2600. Why the difference?

The only way I found to remove parts of ladders is to disassemble
an Atari joystick and hold down buttons together. But it didn't help
in climbing higher. Some extra ladders are created when taking up the
Flame Spirit with you. But it's still not possible to climb as far up as
in the 2600!

What could be the reason for the difference?

--
Tony
t2k.DeleteThis@vcn.bc.ca