I did some testing...
Ceiling figures are generally for when the plane reaches 500fpm RoC. The B-26B in AH with 100% fuel and 8x500lb bombs(happily running at 61in MAP/2700rpm all day), reaches it's ceiling at about 20k. So far, so good.
I dropped 4 of the bombs, shot most of the .50 ammo load off, then the ceiling increased to about 26k. Sounds reasonable to me.
Above 26k the extra-secret-turbo kicked in, and RoC increased again over 500fpm once higher than 26k, but I only got to 31k before the plane started a series of oscillations and could climb no higher. Now that was weird...
With only 25% fuel and most of the ammo gone(Left 200 front guns, 1000 rear turret) and 4x500lb bombs, the ceiling goes up to - suprise - 31k?! The same oscillations started up again, and no higher did I go. Hmmm... The climbrate this time was much higher, starting at 2000+fpm and reducing to 1250fpm at 20k, but it never actually got down to 500fpm by 31k though, so maybe you could manually fly it over 31k, but I didn't try though.