/clear @p writable_book 0 0 {pages:["Look Room"]}
The space between "Look" and "Room" causes a parsing error.
I see this was 'resolved' in an earlier snapshot, but it's still occurring.
Linked issues
Comments 2
Duplicate of MC-44688 - If you have not, please use the search function in the future, to see if your bug has already been submitted. If you could not find the original report, please comment with the keywords you searched for.
Confirmed. I think this happens with any tag that has a space in its value.