This was very rude. You could, and should have, said it in a nicer way. You could have said: I do not believe it is a Mojang-based problem. I think that it is a problem with MCSG's own plugin. I believe it to be the plugin messing up and not completely clearing your inventory. This has nothing to do with mojang, or so I believe. It is, I think, an MCSG plugin problem.
Truthfully though, I'm nearly sure it is a Mojang problem. Though I believe you are wrong, it is actually good to give your opinion, just state your opinion without degrading others in the process.