A_OverlayThink does not handle chains well.

[frozenLake]

http://www.gfycat.com/IgnorantMilkyKingbird

I was retesting my little wad in submissions presently, and discovered this nasty bug originally when playing gravity garden in OpenGL, so I ended up opening SRB2 back up in software mode to see if this bug existed in that renderer, without any other mods loaded. Which it does. So, yeah.

 

[Monster Iestyn]

As I recall, the player's position is shifted for chains *after* all object thinkers have been run, so if A_OverlayThink was used during object thinkers (i.e in states or in a MobjThinker Lua hook) - rather than, say, in a ThinkFrame Lua hook - then it's not really surprising that it happens.

This'll happen for things like A_CapeChase and related too, I'm guessing.