bug with splitPS in Data.PackedString

there's a bug in Data.PackedString that doesn't exist in PackedString:

Prelude> :m PackedString
Prelude PackedString> splitPS ('\t') (packString "Foo\tBar")
["Foo","Bar"]
Prelude PackedString> :m Data.PackedString
Prelude Data.PackedString> splitPS ('\t') (packString "Foo\tBar")
["Foo"*** Exception: Ix{Int}.index: Index (7) out of range ((0,6))

--
 Hal Daume III                                   | hdaume@xxxxxxx
 "Arrest this man, he talks in maths."           | www.isi.edu/~hdaume