The bug:
When you click a sign with a chatEvent, the position where you clicked is not considered. You can click anywhere and the chatEvent is always triggered.
What should happen:
The chatEvent should only be triggered if the actual text with the chatEvent was clicked.
How to reproduce:

• Create a sign with a chatEvent:
  /setblock ~ ~1 ~ minecraft:standing_sign 0 replace {Text1:"{text:\"click here\",clickEvent:{action:run_command,value:\"/say clicked\"}}"}
• Click anywhere on the sign:
  It will print out "clicked" in the chat wherever you click on the sign