How to prevent multi-rate filter from scaling output

I'm using a lowpass filter created with ippsFIRMRInit to upsample a signal by a user definable factor. The output of the filter is scaled roughly (not exactly) proportional to the upsample factor.

Is this expected behavior? If so, how do you determine the correction factor to make the upsampled data look like the original signal?

There's a "doNormal" option for ippsFIRGenLowpass, but there's nothing in the documentation that explains what it does. I tried setting it to both true and false, with no noticeable difference in the output.