RcppParallel with TBB not releasing threads

[ppanko]

For example, running the distance matrix example in the RcppParallel gallery with TBB (but not tinythread) as the backend results in unreleased threads after the program finishes. Tested on both macOS and Linux platforms -- I am assuming this is broadly replicable, but if not, am happy to provide specifics.

Is this behavior intentional and if so, is there an accepted way to release the threads?