This showed up in https://git.opendaylight.org/gerrit/74322 and boils down to:

grouping special-next-hop-grouping {
    leaf special-next-hop {
        type enumeration {
            enum blackhole {
                description "Silently discard the packet.";
            }
        }
    }
}

choice next-hop-options {
    case special-next-hop {
        uses special-next-hop-grouping;
    }
}

SpecialNextHopGrouping generates an inner enumeration class named SpecialNextHop. The case statement leads to SpecialNextHopBuilder being generated, which contains an inner SpecialNextHopImpl implementing SpecialNextHopGrouping.

Since SpecialNextHopImpl implements SpecialNextHopGrouping, SpecialNextHop enumeration shadows the case statement, leading to mismatch in types when SpecialNextHop is used with a short name.