When you slide the finder forward all the way, you should hear a little click as the pin pops up to engage the hole in the finder base. (I don't have a WLF but I assume the engagement is similar to the prism.) It sounds like this is not happening. Probably something is slightly misshapen and either the WLF is not sliding forward all the way, or the hole in the base is a little out of shape or misaligned so that the pin doesn't engage. Take it off and look for dents in the finder or body, crud in the body grooves that would block the finder from sliding forward all the way, etc.