Rocket Jump / Backstep impossible?

[DooMGater]

I made a small map, Doomgates Training Camp , where people can practise wallrunning, straferunning and rocketjump (fire a rocket against a wall direct in front of you and make a step backward) , but this rocketjump seems not to be possible with doomsday? It works fine with vanilla DOOM.EXE, DooM95 and even windoom. Any Idea??

BTW: I am _NOT_ talking about rocket jumps like Q3 - for gaining more height, but about those -flat- rocket jumps, that are only possible with doom...