When you select multiple jars and select remove from a ClassPathGroup, each remove invocation only removes half of the selected items.
So to remove 8 jars, you click remove - 4 are removed.
Click remove again - 2 more removed.
Click remove again - 1 more removed.
Finally click on the last one to remove it.
Actually, this behavior is consistent for all groupings that use the +,- listing.