I do believe I have the most recent release of Aspose Diagram, because when I view my reference to Aspose.Diagram in Visual Studio, the version is 5.9.0
Unfortunately it’s not straightforward for me to provide me a zip of my project as there are confidential db connections, etc. within.
While it does sound like there is a bug, I find it strange that we are seeing different outputs. You are using the following property Shape.TextXForm.TextAngle, correct?
Lastly, if you do not mind, try to export the file to both Visio, and PDF formats – do you see the same result in both cases? I have been using PDF, and I don’t suspect that has any impact, but I would like to know for sure. I had difficulties exporting to .vsdx format, but my end goal is PDF, so I didn’t bother troubleshooting.