Performance degradation in arcpy.mapping when setting text elements

Question

I'm generating a map book of about 300 pages using arcpy, instead of using the toolbox, because I need to do a bunch of scripted actions - on each page I'm setting the extent and rotation of 3 DataFrames, setting the value of 8 TextElements, and then saving the layout using arcpy.mapping.ExportToPDF.

What I'm seeing is that the loop gets exponentially slower the longer I leave it running, and I've narrowed it down to setting the value of TextElements. I've got a simplified example where all I do is

1. Open the MXD
2. Grab a reference to the TextElement
3. Within an endless loop:
   • Set the value of the TextElement
   • Print out the time

Processing the times results in a graph like this:

...and it just keeps getting slower.

Has anyone seen this, and have a solution? Or do I just break up generating my map book into batches of 50-100 pages and restart the script? (which is my current workaround)

Simple example script:

import arcpy
import datetime
import os

MXD_MAPBOOK = r'E:\workspace\data\N&I\N&IMapBook_landscape2.mxd'

def findTextElement(doc, elementName):
    lstElements = arcpy.mapping.ListLayoutElements(mxd, "TEXT_ELEMENT")
    for elm in lstElements:
        if elm.name == elementName:
            return elm

mxd = arcpy.mapping.MapDocument(MXD_MAPBOOK)
dTime = datetime.datetime.now()
elem = findTextElement(mxd, 'baseRailLine')

while True:
    elem.text = 'Test number'
    print(str(datetime.datetime.now()))