In Axis Angle rotation, when X, Y and Z values are absolute 0 (not almost 0, i.e., type '0' in each box), changing value W has the effect of scaling the object. As (0,0,0) doesn't define an axis, it seems that the mesh vertices kinda rotate around origin point, or some weird stuff.

Actually, value (0,0,0) shouldn't be allowed for X, Y, Z boxes at the same time, in Axis Angle rotation mode.

In the attached file, just keep changing the W value, and watch what it happens.

Regards.