It's because gdm flips back to the VT from which it was started (VT 1), shortly *after* usplash is started -- the VT switch killing usplash.
Fixing bug #61529 so that usplash doesn't flip to VT 1 means that gdm is started from VT 8 instead, which is where usplash is running when it terminates -- thus not killing it.
Figured this out.
It's because gdm flips back to the VT from which it was started (VT 1), shortly *after* usplash is started -- the VT switch killing usplash.
Fixing bug #61529 so that usplash doesn't flip to VT 1 means that gdm is started from VT 8 instead, which is where usplash is running when it terminates -- thus not killing it.