How about IE 10 or IE 11? IE 9 is running the old urlblast agent code and 10/11 are using the same code as Chrome (and I’m really close to just killing the old code and using wptdriver for all of IE).
There is similar problem with wptdriver agents. I changed script to combine all steps because with wptdriver agent IE has problem even with logging into the application. My private instance of WPT uses urlblast agents because some problem with wptdriver when testing NTLM authenticated applications. This is main reason I have not migrated yet.
Application itself is written really strangely but it works in modern browsers and I cannot find anything special while debugging with devtools of fiddler.