Can get stuck in slopes (E1M1+others)

[Macil]

I've noticed that I occasionally get stuck in steep slopes in QSS (and vkQuake) in a way that I never do in other ports and the rerelease. Sometimes when I'm trying to jump up onto a surface and land on a steep slope, I get stuck on the slope. Sometimes I get fully stuck, or sometimes I only get stuck in certain directions until I move a specific direction like directly away from the slope. Sometimes the player slowly sinks straight downward through the level geometry and eventually falls out, or sometimes the player repeatedly sinks and then resets upwards a bit while staying stuck.

I think it might be tied to specific slopes in certain maps.
I think it might be tied complex movements like jumping toward the slope and then slowing down or reversing direction in mid-air before landing on the slope. It might be tied to bumping a slope or edge on the way up to get some extra upward momentum before finally landing.

I'm able to reproduce this often while trying to jump on this lamp in E1M1 (specifically in the rerelease). Maybe 1/20 of the times I jump against the slope I get stuck. This happens to me often because you need to jump on this lamp for one of the map's secrets.

I'm stuck in the second screenshot. Here's a save file right there: e1m1-release-stuck-s19.zip. (Note that this is specifically for the rerelease version of the map; the save file doesn't have the same issue if you load it in the original version.)

The player sinks in place and then is reset up a bit frequently. I'm not able to move left or right, but I can move backwards and unstick myself.

If I do the console command "pr_checkextension 0", then I immediately unstick and slide off of the slope as expected.

I've also been able to reproduce this in Ter Shibboleth: Drake Redux:

(showing the area)

(looking at the slope, which leads to a pool of water)

(after trying to jump up the slope to get to the water and failing and getting stuck)

I'm stuck in the last screenshot. Here's a save file right there:
ter_shibboleth_drake_redux-stuck-s19.zip.

The player sinks in place until they're past the floor, and then they fall out of the map. The command "pr_checkextension 0" immediately unsticks the player.

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Tested with 2022-August-11 version.

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I was curious if this was directly related to #50, but my workaround PR #122 for that issue had no effect on these slope sticking saves, so it's probably not directly related.