ArcMap 10.2.1 Export PDF vs arcpy Export PDF scale differences?

[CoryKratz]

I'm experiencing differences from exporting features to PDF from within ArcMap and using a stand alone python program. Basically, I'm selecting a feature from a layer, zooming to the selected extent, changing the scale of the dataframe, and exporting the image to a pdf from PAGE_LAYOUT view- something pretty simple.

The issue that I'm having is that from within ArcMap, everything works fine. In the page layout view, everything looks as expected, and once exported, it looks great.

I'm trying to automate this so after building a stand alone python program, it exports like it's supposed to, however the scale is off by about 200.0.

Here's a snippet of my code:

mxd = arcpy.mapping.MapDocument("C:\Path\To\MxdFile.mxd")
dataFrames = arcpy.mapping.ListDataFrames(mxd)
df = dataFrames[0]

layers = arcpy.mapping.ListLayers(mxd, "*", df)
for layer in layers:
    if layer.name == "LayerIWantToUse":
        break
        
if layer.name != "LayerIWantToUse":
    raise Exception("Cannot find layer.")

arcpy.SelectLayerByAttribute_management(layer, "CLEAR_SELECTION")

query = "OBJECTID = 1"
layer.definitionQuery = query
arcpy.SelectLayerByAttribute_management(layer,"NEW_SELECTION", query)

df.zoomToSelectedFeatures();
df.scale = 2400.0
fileName = r"Python_2400.pdf")
arcpy.mapping.ExportToPDF(mxd, fileName, "PAGE_LAYOUT", 1056, 1632)

The scale that it actually exports, appears to be 1:2200 instead of 1:2400 like it's supposed to. I've attached both images to show the differences.

I have noticed that if I save the MXD with a different scale (1:100000 for example) and with ArcMap in "Data View", I have the scale issues. If I make sure "Layout View" is selected, change the scale to 1:2400, and save the MXD, I do not have the scale issues.

I've seen quite a few forum posts regarding this, some saying it's a bug that should have been fixed in 10.1, but nobody with any real explanations on why there's scale issues.

Has anyone else encountered something similar?