Our current FastFAT has a major memory leak: it leaks any directory that was referenced (used directory and its parent) forever.
Indeed, it references the associated FCB twice on creation and only dereferences it once when it's no longer used. It also doesn't delete any caching associated with the said directory.
How to reproduce? Perform any directory intensive operation and you'll see your memory drop. One good example is trying to unzip ReactOS source code. You'll end with a 0x4D bug check because both FastFAT and Cc will have eaten all the memory.