I have noticed the same behavior, and I believe I have figured it out. (The following does not seem to be documented in any manuals that I’ve been able to find.)
The Bad Bomber Cart becomes available to you when you lose in a 3+ player Battle Game on Maniac Mode. After being eliminated you will appear on the outside border of the arena in a “Bad Bomber Cart”:
There is a default distance that you are able to throw the bombs - 5 “squares” away from the edge of the board:
If there is an obstacle blocking the destination square of the bomb, it will bounce one square further. If that square is blocked as well, it will continue bouncing until it reaches a free spot:
In the above image, the fifth square was blocked (by a standard obstacle) and so the bomb bounced into the seventh square (the first unblocked square after the fifth square).
There is a reproducible way to throw a bomb less than five squares away: If there is a rival bomber that is two, three, or four spaces directly in front of the Bad Bomber cart, then your character is “smart enough” to attempt to hit the rival with the bomb. It does not work if the rival is in the space directly adjacent to the Bad Bomber Cart. Examples:
Two spaces away - Here the rival is seen “spinning” from having been hit by a bomb thrown by Bomberman in the Bad Bomber Cart. The rival is in the second square away from the thrower:
Three spaces away - Here the rival is seen walking away from a bomb that was just thrown at the rival - it landed in the third square away from the thrower:
Four spaces away - Here the rival is seen walking away from another bomb that was just thrown at the rival - it landed in the fourth square away from the thrower:
One space away - Here the rival is seen walking away from the space immediately in front of the Bad Bomber Cart, and the bomb was thrown the default number of five squares away. Thus, it seems it is not possible to throw the bomb only one square away from the Bad Bomber Cart: