Throughout Minecraft, AFK fish farms have been very important, as, on PCs, you can press one button, click t/chat, and the button would keep getting pressed, even if the real-life key wasn't pressed. In the Beta version, this isn't true. Example: I am sneaking, and want to keep sneaking for a long time without me pressing anything. But when I press shift and then press t, but it automatically goes off shift, as in the current 'formal' version, this still applies. If this was an actual implement or a bug, this would really upset the community, and break lots of AFK farms (including fishing).
This is intended as per MCPE-25760.