A custom server is needed to reproduce this issue.

Sending InventoryContentPacket with the creative inventory contents to the client while it has the inventory window open, will cause the game to crash. This is a problem for custom servers (such as PocketMine-MP) which send an empty creative inventory to simulate a Spectator Mode inventory.

This did not happen in versions prior to 1.2.

Perfectly understandable that this issue may be closed as invalid since it pertains to third-party servers, but this bug is caused by something that changed in Minecraft PE between 1.1 and 1.2.