It seems that many different custom maps have the “you were dropped” bug since the previous SCII patch 1.4.2. We expect Activision Blizzard to fix this, since the map developers can’t do anything. Nevertheless, we have a guide on how you can avoid this bug:
Before you join a lobby and invite people directly to the game, you should form a group (create a party) and invite everyone who wants to play to your party. Then, join the lobby all at once and start the game immediately after. If you wait too long in lobby, the host will most likely get dropped from the game right after start. If you want to play with more than 6 people, create a party with 6 of them (since it’s the player limit for a group) and then join the lobby. After everyone has joined, invite the remaining players and start the game as soon as possible.
The risk of getting dropped from the game rises with the time you spend in the game lobby. This should help you to avoid this bug for most cases.