[C# MSCE 10.14] Change sheet number & name programmatically

I'm trying to change the sheet number & sheet name of a sheet model programmatically using the code shown using DgnPlatformNET.

When I look at the sheetdefinition after I assign new values it shows the correct values, but checking after I save the model settings they are back to the original values.

DgnFile dgnFile = Session.Instance.GetActiveDgnFile();
DgnModel dgnModel = Session.Instance.GetActiveDgnModel();

ModelInfo modelInfo = dgnModel.GetModelInfo();
Bentley.DgnPlatformNET.SheetDefinition sheetDefinition = modelInfo.GetSheetDefinition();
sheetDefinition.SheetName = "My Sheet Name";
sheetDefinition.SheetNumber = 100;
dgnModel.SaveModelSettings();
dgnFile.DoSaveTo(dgnFile.GetFileName(), DgnFileFormatType.Current);
modelInfo = dgnModel.GetModelInfo();
sheetDefinition = modelInfo.GetSheetDefinition();  //back to original number & name values, not what I added

Any ideas what may be wrong?

I attempted the same using COM Interop and get the same results.