The documentation in the 4.5.0 and lower JavaDocs is incorrect. This has been updated in version 4.6.0+.
Here is are a chart on how it works.
PRIORITY in the Tasks Application
Normal -> 5
High -> 1
Low -> 9
PRIORITY Specified to setInt()/addInt()
Normal -> 0, 4, 5, 6
High -> 1, 2, 3
Low -> 7, 8, 9