Well, trying to figure out what's going on I found this in the doc:
Table 18-6. Compare Output Mode, Fast PWM Mode(1)
COM2B1 COM2B0 Description
0 0 Normal port operation, OC2B disconnected.
0 1 [b][i][u]Reserved[/u][/i][/b]
1 0
Clear OC2B on Compare Match, set OC2B at BOTTOM,
(non-inverting mode).
1 1
Set OC2B on Compare Match, clear OC2B at BOTTOM,
(inverting mode).
So I guess this is my answer!!!