Hi,
We actually don't block any feature. The code you see it the code for backward compatibility. Back in the history, a year ago (Meta Box 4.12), we created an abstraction layer for storage. This layer allows us to interact with many storage in WP easier, such as term meta, user meta, settings and custom table. Without it, we had to created many filters just for saving and getting the values.
Since then, we have updated all the extensions to use this feature, including Group and Term Meta. I'd suggest you update the group extension to the latest version 1.2.16. What you're having is 1.1.5, which behind 18 versions. And Meta Box core plugin is now 4.15, 3 minor versions have been released.
Update: I found a quick and dirty fix for MB Term Meta that makes it works with old version of Group. Please update to version 1.2.3.