Keyword exists but does not work for new entries

There is a keyword called "reference-to-dennis-rader-(btk-killer)" but parenthesis are not valid in keywords. Yet, there are four titles attached to this keyword.

Here's the error:

This keyword probably should just be reference-to-dennis-rader-btk-killer. There are already keywords for reference-to-dennis-rader and reference-to-dennis-lynn-rader. Can we get themm all combined into reference-to-dennis-rader-btk-killer?