Just today I was on the siege server and typing out a particularly long message (I type rather slowly) so I wasn't moving. Somebody reported me for leeching, so I felt kinda bad when i had to make him lose a multiplier. It made me feel like an ass, really. If anyways, pushing any button (perhaps one of the WSAD keys) would prevent people from doing this while someone's in combat, because most likely they'll be moving around (with WSAD, or SD if they use ESDF setup).
If anything, using the 'report leecher' thing should send a message to admins (assuming what you say is true and an admin is on) so they can go check it out themselves. Perhaps even make the "show names cheat" more useful since they get the name of the leecher they can immediately go and check it out without having to go spectator.
Also, the other day I was reporting someone as a leecher, and apparently it was reporting Goretooth (who was trying to actively chase down an enemy cavalry) so I don't know what's up with that.