This is a bug of Foxit PDF IFilter 2.1 and 2.2. And it has been fixed by Foxit PDF IFilter 3.X.
To fix this bug, please do as follows.
1) Upgrade your IFilter to version 3.X.
2) Activate Foxit PDF IFilter with a valid license (code/license key).
3) To make the changes take effect, do an IISreset, stop and restart search service.