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Somewhere between ZDoom 2.3.1 and the current trunk, the drop style of some items, such as Zombieman's Clips, was altered so that they spawn at about the monster's half height with a slight +z velocity, to then fall down. This is different from 2.3.1's behavior where the clip is spawned nearly at their feet with a z velocity of 0.
Looking at commit 1812, and changing wadsrc/static/mapinfo/doomcommon.txt to have "defaultdropstyle = 2" instead of =1, I get the 2.3.1 behavior back, which seems to be more in line with what prboom-plus produces.

There's a compatibility option for this under the options menu I believe. Try searching for it.

Snarboo wrote:There's a compatibility option for this under the options menu I believe. Try searching for it.

Correct. "Spawn item drops on floor", 8th one down (not counting the overall compatibility preset).

Is anybody aware of why this change was made?

No change was made. The default was always like this. Apparently some option got switched in your config

Well ok, I tested. In ZDoom 2.3.1 with a blank config (i.e. no config), drop-at-bottom is set to NO by default, yet the items are spawned near the bottom. I thus take it that it was a bug.

OTOH, I mentioned prboom-plus. Assuming it reproduces Doom2 behavior, ZDoom's drop-at-bottom=NO is non-standard. Not that ZDoom would not have many non-Doom2 default settings, but it does have some (like always_mouselook=false by default), so the question would be where to draw the line.

Doom's Spawn at bottom is useless in a z-aware engine. In particular it screws up miserably when some monster dies on any kind of solid 3D struture, be it invisible bridge things, 3DMidtex textures or 3D floors.