Path Animation Camera Angle issue (or not))

Good day. I’m trying to do a Path Animation with Camera angle different from zero on Rhino 5 SR14 x86 and facing this thing: camera rotation angle is changing throughout the frames. Moreover, the more i messing up with camera rotation angle on a different “frames” via “Preview frame number” menu item (trying to fix it) - the more unpredictable behavior i’ve got. For instance: if i change rotation angle in the first frame - it changes ok, and affects whole animation, but growing constantly, till the end. If i change the angle in a mid-frame to correct value - the first frame angle got messed up and whole frames camera angles with it - to the value not even close to initial (and right). Both path and target curves flat, concentric half-circles (180 degree arcs) located one above other on a parallel planes.
So questions are: is it normal behavior? Is there any way to lock camera rotation angle somehow? Thanks.

PS with zero rotation angle no problems, it is not changing throughout the animation.