The generated signature of a generic type (as an argument) is incorrect, therefor the on-hover description is not shown.
I'll fix it this evening @ git, but in the meanwhile, here is a quickfix:
In Extensions.cs
Find:
public static string AsSignature(this Type target, bool fullSignature)
{
string signature = target.FullName ?? target.Name;
Add:
if (target.FullName == null && !target.IsGenericParameter) { signature = target.Namespace + "." + signature; }
This should fix this issue. Seems to work just fine for me.