When you export cameras, there is a conversion from focal length in mm to vertical (or horizontal) fov in degrees. This conversion happens properly for static yfov values and for key values, but it is not being done for key tangent values. I have put a hack in my code to convert the tangents, so it’s not critical for me.
The other problem seems to be in the importer. Any time I import a .dae with cameras, the focal length comes out wrong (even when not animated). It seems that non-animated cameras always get imported as 35mm, and interestingly, animated cameras have correct key tangents, but incorrect key values.