can't change camera's fovMode at runtime

hi everyone.

i'm not sure if it is a bug, but i can't change camera's fovMode without changing fov parameter also.

i have a radiobutton that toggle fovMode between VERTICAL_FIXED and HORIZONTAL_FIXED and a slider that modulate the fov parameter.

if i select a fovMode, i have to manually slightly change the fov parameter to see the effect on screen.

why?

thanks everyone!