In N4910 [over.call.object] paragraph 3, note 1 (in part) says:

The conversion function from which the surrogate call function was derived will be used in the conversion sequence for that parameter since it converts the implied object argument to the appropriate function pointer or reference required by that first parameter.

This is not true. Overload resolution can prefer a different conversion operator because the conversion function from which the surrogate call function was derived is not the best viable function. See https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81547.