It looks like a few bugs snuck into the latest release of the Real Statistics Resource Pack, Rel 8.9. The purpose of this release is to address these bugs. At the same time, a couple of new features have been added. In particular, Rel 8.9.1 addresses the following issues:
Bugs in the new Homogeneity of Variances data analysis tool have been fixed.
The MW_TEST worksheet function has been enhanced to provide an option to use the rank-serial correlation as the effect size for the Mann-Whitney test.
The OBrienTest worksheet function has been enhanced so that blank elements are ignored.