Hopefully a relatively easy one to answer. :) My bathroom door has a standard hinge attached, that requires the door to physically be closed - this matches the setup of the other doors in my house. However, when fully opened, my bathroom door closes up to a certain point and then stops - this amount is consistent each time. What causes this to happen for certain doors, and not others? This is the only door to do this in this house, but I've seen others that have done something similar previously.
The two hinges are not exactly one above each other, in 3D. One of them is slightly left, right, front or back, relative to the other.
As such, the line going through both hinges forms a vector in space. If this vector is not straight up, when the door rotates around it, the door will go higher or lower.
Gravity is pulling the door down. As such, it will try to go to the position where the door is lower.
(following comments, I assumed passive hinges. Do you have a hinge that is supposed to close automatically?)
The most likely causes are a tilt in the wall or a poorly hung jamb. In either case the hinge jamb is out of plumb. In your case it's leaning toward the center of the door swing. The door slab is actually lower in that partially-open position, so that's where gravity puts it. This is more common with solid-core doors, which are much heavier and therefore overcome hinge pin friction more easily.
An old hack is to pull the hinge pins one at a time and bend them. Lay them between two blocks of wood and give them a pop with a hammer. Start with about a 1/8" bend in each hinge. This may introduce enough friction to counter gravity.
The right fix is to actually re-hang the door. However, if the lean in the wall is severe enough, you won't be able to hang the door plumb and not have a substantial misalignment, which pays heck with the casing.
If you care to investigate with a 4' or longer level, report back and we'll address it further.