Test AutoWriterCompressionTypeTest fails on TYPE_BYTE_GRAY

Mac OS X 10.7.4 macmini4,1
This test, AutoWriterCompressionTypeTest, reads an image then writes it, reads again and does compare this read image to the orignal using certain GeometricMomentImageComparator with criteria center shift 1, relative error 0.25.
It fails only with TYPE_BYTE_GRAY writing gif (lzw compression). If it's TYPE_USHORT_GRAY, it works. It also works writing jpeg.

Note that written image looks compelling enough, so the difference should be rather subtle.