both 1.1 and 1.2/GPP:
Jumping off a wall increases your overall velocity by a bit (can't remember the value) and adds (not sets) velocity away from the wall and also adds upward velocity to your current velocity.
There is a jump timer restriction that restricts your ability to spam the jump and that time is 200msec as DevHC pointed out above. In the time you cannot jump again and cannot walljump. This is partically significant for the the differences between 1.1 and GPP style marauder:
1.1: Your velocity isn't clipped for the 200msec duration after you last jumped.This means you can jump before a wall and your velocity will not reduce until the 200msec timer is done. However before you can jump again, your velocity is clipped (the velocity component into the wall is set to 0 basically) and you jump off it. This is why you do not stick to a wall, but you can jump at a corner at a fast horizontal speed, and you sort of "warp" around the wall without losing any speed if the time you collide with the wall is less than 200msec after your last jump. This is actually a feature in CPM physics.
1.2/GPP/Unvanquished: Same as 1.1 except your velocity gets clipped AFTER the next jump when the 200msec paralising period is done. If you decide to jump again, the timer just resets and your velocity doesn't get clipped and if you had enough velocity into the wall when you started, enough to overcome the walljump velocity added away from the wall, you get the "Sticky" feeling. Because the Marauder's air accelreation value is higher in Unvanquished and KoRx (adv mara) and when using the CPM bunnyhop strafe acceleration (A/D keys) than in 1.1, the marauder's acceleration is greater than the overall acceleration away from the wall as a result of walljumping. This is why you can basically climb a wall in maps like the Cannon series.
Note that the jump timer bug ALSO exist in other forms and not just the marauder.
One example is the human dodge ability in GPP and Unvanquished, where after using the dodge function, your velocity doesn't get clipped horizontally (and friction becomes 0 above a certain sv_fps value in some maps like yalt's star atcs) which means you are able to sort of "slide around"
Watch the speedometer in the unvanquished vid samples below:
(I just used u2b's brighten-up function for this new upload)