You can build momentum by pressing up against a wall

[happygreenfrog]

You can still build momentum while pressing up against a wall. This is able to be observed by comparing Diamondus 1 in both OpenJazz and the original Jazz Jackrabbit, pushing up against the wall while bouncing up the first spring in the level, then letting go of the right key just before you reach an area that doesn't have a wall. In Jazz Jackrabbit, you'll bounce straight up, in OpenJazz you'll continue going forwards and land on the platform above.

As a side note, the running animation also continues to play when pressing up against a wall, which is probably related (in the original game it would only play the walking animation).