Although the Details Panel shows the degrees wrong, the object seems to have done it's rotation correctly but not in the right degrees. It will rotate to the position specified but it goes the wrong way in the calculation of the Detail Panel or the vector.
When reproing this, rotating the BSP with the pivot rotation past 90 degrees on the Y axis also changes the rotation of the X & Z in the Details Panel but there isn't a noticeable change in the viewport.
This was reported and tested in 4.23.1 (CL-9631420). This was reproduced in 4.22.3 (CL-7053642), 4.24 Preview 1 (CL-9979423), and Main 4.25 (CL-10069919)
Results: At Y = 90 ° and a rotation on Z axis of 5 ° using the snapping tool, the other axis show the following result vector -> x = 85.0 °, Y = 90 °, Z = 90.0 °
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-83363 in the post.