When Garbage Collection runs, all binaries older than x time get deleted, regardless if they are in use or not.
2 problems I detect:

• Deleting a file node will not mark the binary as unused
• Garbage collection query does not take into account the usage_flag: DELETE FROM content_store WHERE usage_time < ?

Attached unit test demonstrates this behaviour. Note that with the use of FileBinaryStore, the test fails as well, but has different behaviour (see test description)