That's a weird one, Robert, can't say I've seen that issue before.
Try the following:
Copy all the text from your title
Click the reset button in the bottom left of the title
Then edit the title again and paste in the text
See if that helps? If the problem is the same, rather than pasting, build up the title again with all the fields from scratch?
I did some further testing. The editing limitations were encountered after the Title object was changed from tiled to floating.
Unchecking the Title’s Floating option did not help. Removing the Title and adding it back in did not help either. Choosing “Reset” did work and I created the title from scratch as a Tiled object.
It is important to note that the title could NOT be edited after copying from the original and pasting into the new, even if the new was reset and tiled. My only conclusion is the something in the original title became corrupt and did not allow adding additional characters, spaces.