I tried saving a template from my 5.1 site and installing it on a 5.0.8 site. It gives an error that says the template file is not properly formatted.
It may be normal if 5.0.8 is not expected to read templates from a future version. If however the template format has not changed then this could be in issue.
The templates in question were for things created while the site was still on 5.0.8 before I updated to the 5.1 beta. They did not have sliders or any other changes under 5.1.
To resolve the issue I removed 5.1, installed 5.0.8, and I was able to download and install the templates just fine.
This is only an issue if all 5.X templates sre supposed to be compatible. Anyway, just thought you should know.