When Clicking Settings -> Canned Messages and trying to insert or delete text in any of the canned messages, after the first key press, the cursor moves to the end of the text already there.
Editing the Welcome Message, if it currently reads:
Hello, you've reached Joe
and you want to edit it to read:
Hello, this is Joe
When you click to place the insertion point after the word "reached" and press the backspace key, it will delete the last "d" and then jump to end of the text (after "Joe") and start deleting text from there. This means you can only edit the text in the canned messages by deleting everything from the end of the text, back to where you want to start inserting text.