Depending on the insertion order of folders which is non-deterministic
because it relies on the kernel's scheduling of parsing threads, the
listing the user sees might not be up-to-date because later thread
updates are never broadcast. This results in inconsistencies between
threads and mail listings when a thread's root envelope was part of a
not broadcast update leading to `key not found` panics in a listing's
hashmaps.
Manos Pitsidianakis