MF_SOLID collision breaks with objects that have a radius greater than 64*FRACUNIT (like 128*FRACUNIT)
When walking to the outer edge of an object with MF_SOLID and a large radius (around 128*FRACUNIT or larger), it suddenly jumps to the top of your head, causing you to fall under it. And you can continue you push it upwards in that same outer edge if you jump or fly or whatever.
This is absolutely infuriating to me, as it prevents me from creating large splat platforms that properly function as platforms in level design. Instead, they yoink themselves out from under your feet, making you unfairly fall into a pit.