[Grunt]

I ran into the same thing awhile back with this mod - yes it is the borders defined in alt1/2 tags.

Instead of losing your alt borders throughout your forums just for this mod (unless it's of no consequence), create two 'Additional CSS Definitions' that are duplicates of your alt's minus the borders, which more than likely only leaves the background color. Then, in your postbit_legacy template replace all instances of alt1 and alt2 with the newly created definitions.

.alt1a {background-color: #F5F5FF;}
.alt2a {background-color: #E1E4F2;}

Or something along those lines..