The World of Avlis

My char has str = 10...
+ Ring of Hill Giant Str. (+2) -> STR = 12
+ Maximized Bull's STR (Max(1d4+1)=5) -> STR = 17
+ Maximized Tenser (Max(2d4) = -> STR = 22...?? - Why...?

The same situation is when i take this ring off, STR = 15 after Max Bull's STR, and after Maximized Tenser, STR = 22....