The library manager does not allow you to put a space in the name of a library that you create manually, yet Java libraries that come bundled with Netbeans have spaces in them.

This leads to having to use CamelCase for naming, which is harder to read.  It should be simple to allow it, since it obviously is able to handle such names.  My guess is that there is a check for manually added names that simply is not needed, where it might have been needed in the past.