Very new and rare bug o.O

Ok so in my game I have it where if you press either C or . the player shoots an arrow. For some reason, when you hold it down, and press ANY... I mean --ANY-- key on the keyboard, while holding down C or ., the arrow will shoot o.O
Repeat is set to off.
holding down any of the fire-keys will make the arrow only shoot once.
Holding down any of the fire keys and pressing another key at the same time, will cause the arrow to shoot o.O
The same thing happens with my jump key o.O
EDIT:
this only seems to happen when you have Multiple Keys able to be pressed.. o.O
Repeat is set to off.
holding down any of the fire-keys will make the arrow only shoot once.
Holding down any of the fire keys and pressing another key at the same time, will cause the arrow to shoot o.O
The same thing happens with my jump key o.O
EDIT:
this only seems to happen when you have Multiple Keys able to be pressed.. o.O