GA-965P DS3 won't boot OS when USB key is inserted

[mihies]

Hi guys,

Mobo: Gigabyte GA-965P DS4 v1.0, F6 BIOS
I wonder if anybody have the same issue: if I leave my USB key connected then OS won't boot - it just stops before OS should start boot process.
I don't have USB as a boot device set.

Any idea?