Revit has 16 lineweights. They say that the lineweights should be constant no matter what scale your drawing is at. We've found that's not always true. Go to Settings... Lineweights... and you'll notice that Revit has lineweights setup for 6 View scales from 1" = 1'-0" to 1/32" = 1'-0". Well what happens if you have a drawing at 1:50? Revit uses the closest thing (1/32" in this case). The good news is that you can ADD scales that Revit doesn't have setup. The bad news is you'll have to plot the 16 lineweights after you've setup your new scale and compare them with the default scales to get the settings right.
Maybe in a future release Autodesk will setup their default.rte file with the appropriate lineweights for all default scales.