This is supposed to be common and might be related to Gimbal Locking. When parts are rotated (with the move tool, it’s by CFrame), the Orientation and Rotation are assigned values from the new CFrame of the part. There are multiple ways to represent the same rotation and sometimes Euler Angles will not rotate an object properly without other changes being made (such as flipping the other axis). If you want to use the rotation values from the object, I recommend calculating your own from the CFrame, calculating them from the directions, or other more reliable methods like storing the rotation as you manipulate it. This video might help with understanding why these changes in the values were made. In the video 2 axis were rotated by 90 degrees in order to perform the rotation.