http://bugs.winehq.org/show_bug.cgi?id=26549
--- Comment #2 from Artem S. Tashkinov t.artem@mailcity.com 2012-01-15 14:36:52 CST --- I don't think this bug will ever get fixed, unless it's fixed in POSIX.
POSIX allows user space applications to lower their niceness but you cannot raise it (you will receive the "permission denied" error).
In Windows it's possible to restore "niceness" to the "Normal" level.