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Can't be fixed without editing the game's code itself. The FoV isn't clamped properly, so when the FoV hits an incompatible value it goes into the negative, which causes that flip.
Only real way to avoid it is to play with the lowest possible FoV Source/HL2 supports, which to my knowledge is usually 54. I know that the aspect ratio of your display also has an affect on that number, but you'd have to play around with the fov and fov_desired commands to make it work.