Enchant spell checker doesn't accept numbers

Enchant seems to have a problem with numbers with more than one digit. For example, the command

echo The quick brown fox jumps over 12 lazy dogs|enchant -l

should return all misspelled words and it returns 12. Locale is set to en_US.utf8, but the problem seems to be the same in POSIX locale as well.

ProblemType: Bug
DistroRelease: Ubuntu 11.04
Package: libenchant1c2a 1.6.0-2
ProcVersionSignature: Ubuntu 2.6.38-11.50-server 2.6.38.8
Uname: Linux 2.6.38-11-server x86_64
Architecture: amd64
Date: Thu Sep 29 09:05:19 2011
SourcePackage: enchant
UpgradeStatus: Upgraded to natty on 2011-04-28 (153 days ago)