When you open the chat menu with a block in your hand, that block will be placed as long as you are positioned so that it could be placed normally.
NOTE: This also affects Android, as my Droid X2 is affected as well.
Linked issues
is duplicated by 9
MCPE-2664
When you press the chat button, it places a block in the spot you touched
Resolved
MCPE-2921
Chat button performs tap screen action when using split touch
Resolved
MCPE-4047
Blocks are placed after you hit the chat button
Resolved
MCPE-4184
Tapping chat button places blocks in split-touch mode
Resolved
MCPE-4235
Block placed when pressing Chat Button
Resolved
4 more links
Confirmed.