Yes, it’s “correct” inasmuch as it’s what happens, but it’s not necessarily useful. As I say, we make it possible to set a small positive offset value so that you can bring these items closer to the following notes if you wish. The offset is added to (or subtracted from) the nominal width of the column as an extent, so that is why more rhythmic space is allocated, but because the clef is considered to be on the left rather than on the right, it will not be considered for collision avoidance with items to the right.
The reason that key and time signatures behave differently to clefs is that clefs are attached to notes, and have an impact on the overall size of the left-hand extent of those spacing columns, while key and time signatures are spaced rightwards.
It is indeed (on its face) incorrect that the effect on the overall spacing is not recalculated immediately when you offset a key or time signature. I will check this with my colleagues in the team.