Again its to do with a camera having a target, and the camera won't zoom in when getting close to a target.

Blend for Visual Studio 2013 has support for 3D transforms and animations. After VS Blend 2013 the support for 3D was dropped. :(

Does not seem to work with helix toolkit, so I go back to the regular viewport3D.

I think the reason for this is the camera has a target. So its zooms in and out from a target. When you get close to a target it stops. I seem to remember a walk around mode.

I have found that if I add ZoomExtentsWhenLoaded="True" that I do not get this problem.

I think its to do with the Tab Control. See if it works outside of the tab control.