"gamemode 1" is a command to put yourself into creative in multiplayer.
This "trick" of joining a server, and pretending you are have changed your game mode, or are in creative has been around a long time, and used by players trying to get staff to adjust their gamemode, putting them into creative.
We have had this technique used countless times over the last few years of running this server. I'm sure that it may work other places, but it does not work here. This happens a few times a month, and bubbahunter10 joining at the exact time as another player attempting to do the same thing I believe is more than a coincidence.