Not sure if this is a bug or not so just require clarification as to what is supposed to happen when you use option-click on a triangle in the library window.
With just the headings displayed (English Tools, Greek Tools etc) using Option-click opens everything. This is as expected.
When you use Option-Click again virtually everything disappears including the standard headings. The only way to get them back is to then click on 'Show All'. I would have expected it to still display the headings 'English Tools' etc. although maybe that is not the intention.