When using any other theme aside from the "Classic" one there are two things that are a must in order for them to run correctly on both install and uninstall/modify:
- the Enhanced User Interface should be set to "Always(install, uninstall and maintenance)" in the Themes
page --> Settings --> User Interface.
- your package should be an EXE since the Enhanced User Interface used for these themes is handled by our EXE bootstrapper. You can find this option in the Builds
Page --> Package Type.
Please check these and let us know if you are still encountering issues.