Fix handling multiple groups with wrap

[Khush-dev]

No description provided.

[kizzx2]

Thanks! Is there a schema / test case that would serve as motivation of what situations this would fix?

[Khush-dev]

For the first commit, i put up some testcase which failed without the patch.
For the second commit, iirc, decoding doesn't work with primitive types i.e. you always need to define the primitive as a custom type.