Not sure if this is known, but when dual wielding, both guns will take the reload speed of the primary (right hand) gun. I have tested this with multiple guns.
Pistol.M9.txt
FlareGun.txt
Python.txt

Another bug, occasionally, the second gun will stop working properly, and trying to fire it will fire the main gun instead. It's fixed by swapping weapons but can still be a minor nuisance.

Thanks for reporting, we'll look into it.
For clarification, when the second gun stops working, does clicking the correct mouse button fire the main gun and not the secondary?

yes, it does.

Apologies for the delay, the dual wield is currently fairly low priority, so it's unlikely we'll be able to get to it for a while. Sorry about that.