LTM VS padding payload response with whitespaces and asterisk

I have an application that talks to an old OpenVMS system, which was problematic in permanently closing TCP connections. To resolve this issue, I have put a BIG-IP Virtual Server in between them, so the message flow is now:

webMethods --> BIG-IP LTM --> OpenVMS server

This has resolved the TCP connection issue, and I thought everything was good.

However, the application sends XML, and the VMS system responds with the XML payload.

For some reason, BIG-IP is padding the response with lots whitespaces and one asterisk *

The webMethods server does not expect the * in the response and fails to process the response to the client (who originally sent the XML).

 So why is BIG-IP adding the * to the response payload?

I've included a WireShark trace image, which shows the BIG-IP VS 10.1.4.170 responding to the webMethods server 10.1.4.225, with the payload, including lots of HEX 20 (whitespace) and one * at the end.

My VS configuration uses Type Standard with all the defaults, except, of course, that I've configured the Destination Address and Service Port (3012) and added a Pool.

The closes F5 article I have found is this one:

K44201501: BIG-IP is padding HTTP response with additional whitespaces
https://my.f5.com/manage/s/article/K44201501

However, I don't have Analytics configured on this VS, and I don't have Application Visibility and Reporting (AVR) provisioned. So, this doesn't apply, but it's a similar issue.