Unable to edit custom camera sensor size

[rawbsterlobster]

For some reason when I choose to use the custom camera in the focal length tab, the dimensions revert after changing one value. I either get the preset camera values or they don't change at all.

[eebee2bee]

I realize this is an old question, but I recently had this same problem. Eventually I realized that when manually entering the image sensor dimensions in fSpy, you must hit 'enter' after each value. Don't just click to the the next field or your input will revert to the initial value.