The clickEvent property of JSON text is supposed to allow you to trigger things when the displayed text is clicked. But when used with text for the /title command, it doesn't, though it displays fine otherwise and throws no errors.

To Reproduce:

1. Put this in a command block:

/title @a subtitle {"text":"Click here to continue.","underlined":true,"color":"blue","clickEvent":{"action":"run_command","value":"/say Oh, hey, I continued!"}}

2. Trigger the command block.

3. While the subtitle is displayed, open the chat to unlock your mouse, and click the title text. Nothing happens, whereas the clickEvent clearly should trigger a message in the chat.