Not sure on the XML (... and really don't want to switch my code / feeds to XML)
I have worked around the issue, but don't really understand why it didn't work, if it's a bug on my part or a bug in core Roku code. (All code compiled / executed)
The poster screen performs an HTTP request and shows an updated image if I modify the value in the roAssociativeArray this way ...
movieInfoArray[i].AddReplace("HDPosterUrl", movieInfoArray[i].HDPosterUrl + "?" + m.cacheBuster)
The poster screen shows an old cached image if I modify the value in the roAssociativeArray this way ...
movieInfoArray[i].HDPosterUrl = movieInfoArray[i].HDPosterUrl + "?" + m.cacheBuster