In my tests, setting the Padding value to 0, then hit enter (or moving focus away), keeps the 0.
If I "Clear local value" (or middle mouse click the value), it restores the default style value (wich is 8,7).

Is that what you're experiencing?

This is the expected behavior, because when there is no local value set, the property effective value uses the one with more priority, the default style value in this case.

Please see video. Setting 0 and pressing enter restores the default style.

image.png (10,011 bytes)   

image.png (10,011 bytes)