If you start firing an automatic weapon with hipfire and while still firing enable the iron sights, there is a short interruption in firing.

Wondering if this is a bug or an intended feature.

Probably intended, you wouldn't want to be firing a gun while lifting it up to your eye, good way to get a broken nose or eye-socket.

why whould you do that? from realism point of view youd probably do yourself an eye injury. from gameplay point of view it seems likley thats deliberate unless it does it in a weird way

It definitely doesn't look intended. It looks really twitchy and the model sort of teleports slightly, doesn't move smoothly as it does when not firing. Realism is a non-issue in the matter.

i heard there was a support forum now. haven't looked myself try going back one breadcrumb level and having a look

there is
http://www.gamesas.com/index.php?/forum/139-brink-hardware-and-software-issues-subforums/