My Monk is Level 13. She has a swift weapon in the main hand, “Boots of Haste” and the “Belt of Battle Skill”. A level 13 monk should get 2 extra attacks with the “Flurry” option, but I always got only one extra attack. So I looked into it.
Base Attack Bonus of the „normal“ melee attacks of the main weapon:
+13
+13
+13
+8 (=13-5)
+3 (=13-10)
It is as it should be.
Base Attack Bonus of the „Flurry“ melee attacks of the main weapon:
+9
+9
+9
+9
+9
+9
That‘ s it. And it is weird.
I think, that the “Belt of Battle Skill” should give its bonus to the Flurry attacks too. Otherwise there’s no point for monks to use it.
Besides, in the small mouse-over preview with the success probability, the shown success probability of the Flurry attacks is the same as in the normal melee attack. So there is definitely somewhere a mistake.