if the module has a interface, when i click build solution, it always rebuilds

recently i suffer the problem of rebuilding everything even when i do nothing with my code

i find the interface is one of reasons, an example like this

module inter
    !interface itf
    !    module procedure:: op
    !end interface
contains
    subroutine op
    end subroutine op
end module inter

program main

end program main

if without the interface, clicking <build solution> throws the message 'up to date'

but once the module has an interface, visual studio always rebuild the file when i click <build solution>

is there any way avoiding this situation?

it takes me too much time when debugging my project!

i use psxe2017 updta2 and vs2015