PSA: New trick to ban yourself. Please read.

Anyway I think the Equip window requires server communication because the server has to tell the client which items are truly equipped and which should be reddened out. Although I would think the client already knows, otherwise how would it know how to draw you?
Also, if you don't have your pet out, the pet HP/MP potion slots need to be cleared (idk why, I wish it wouldn't do that, but it does).

Maple's not a great client for questions of "what should be going on". The equip window opens fast enough that I doubt it's waiting for a response from the server.

It's probably clientside hacking tool checks going wrong, in the vein of the disconnection for attacking too soon after you enter a map.

Anyone feel like testing it with equips mapped to a key other than E? I'm too lazy to make up new accounts.