I found and fixed the bug, FYI the problem is caused by the fact the when 'f' is ivoked as a tailcall, the closure is delete when the caller stack is collapsed. Now I keep a strong reference of the closure in the call stack. No biggie, quite an obscure bug though.
I'll release a 2.2.1 tonite or tomorrow as soon as I'm done with the tests.
ciao
Alberto