This is a one of those rare instances where a regional airport with limited runway options is forced to curtail flights for a window of time. Due to the fact that the maintenance that needs to be performed is at the intersection of SBN's two major runways this creates the problem at hand. It is unfortunate that runway 27R-9L is only 4300ft long and 75ft wide. Obviously if it wasn't for those dimensions they would have a backup and prevent this partial shutdown.
This report claims however that the Continental flights will be using that shorter and narrower runway anyway. Having just browsed my OAG Flight Schedule book for August I see that those flights utilize the B1900.
Airport Runway Closures Leave Passengers Confused