Union objects are generated incorrectly when using bits type

I have defined following model:

typedef port-state-v13 {
description
"Current state of the physical port. These are not configurable from
the controller.";
type bits {
bit link_down

{ //description "No physical link present."; position 0; }

bit blocked

{ //description "Port is blocked"; position 1; }

bit live

{ //description "Live for Fast Failover Group."; position 2; }

}
}

typedef port-state-v10 {
description "Current state of the physical port. These are not configurable from
the controller.";
type bits {
bit link_down

{ description "No physical link present."; position 0; }

bit blocked

{ description "Port is blocked"; position 1; }

bit live

{ description "Live for Fast Failover Group."; position 2; }

bit stp_listen

{ description "Not learning or relaying frames."; }

bit stp_learn

{ description "Learning but not relaying frames."; }

bit stp_forward

{ description "Learning and relaying frames."; }

bit stp_block

{ description "Not part of spanning tree."; }

bit stp_mask

{ description "Bit mask for OFPPS_STP_* values."; }

}
}

typedef port-state {
type union

{ type port-state-v10; type port-state-v13; }

}

Code generation succeeds, but compilation of PortState object fails due to incorrect method call: