Duplicate Workers entries in some EXPLAIN plans

Hello,

I ran into an odd behavior with some EXPLAIN results in Postgres 11.5. I
noticed this with JSON format first, but similar issues exist with the
other formats as well for this query. I think I can follow up with the
query and full plan if needed, but essentially, the issue is that the Sort
node has two different entries for the "Workers" key (something that
technically JSON does allow, but such JSON structures are very difficult to
work with, and JSON library support for them is poor). The node looks like
this (some details elided):

{
"Node Type": "Sort",
...
"Workers": [
{
"Worker Number": 0,
"Sort Method": "external merge",
"Sort Space Used": 20128,
"Sort Space Type": "Disk"
},
{
"Worker Number": 1,
"Sort Method": "external merge",
"Sort Space Used": 20128,
"Sort Space Type": "Disk"
}
],
...
"Workers": [
{
"Worker Number": 0,
"Actual Startup Time": 309.726,
"Actual Total Time": 310.179,
"Actual Rows": 4128,
"Actual Loops": 1,
"Shared Hit Blocks": 2872,
"Shared Read Blocks": 7584,
"Shared Dirtied Blocks": 0,
"Shared Written Blocks": 0,
"Local Hit Blocks": 0,
"Local Read Blocks": 0,
"Local Dirtied Blocks": 0,
"Local Written Blocks": 0,
"Temp Read Blocks": 490,
"Temp Written Blocks": 2529
},
{
"Worker Number": 1,
"Actual Startup Time": 306.523,
"Actual Total Time": 307.001,
"Actual Rows": 4128,
"Actual Loops": 1,
"Shared Hit Blocks": 3356,
"Shared Read Blocks": 7100,
"Shared Dirtied Blocks": 0,
"Shared Written Blocks": 0,
"Local Hit Blocks": 0,
"Local Read Blocks": 0,
"Local Dirtied Blocks": 0,
"Local Written Blocks": 0,
"Temp Read Blocks": 490,
"Temp Written Blocks": 2529
}
],
"Plans:" ...
}

YAML and XML formats both have parallel issues. TEXT format is a little
different but also seems odd, with multiple lines in the plan node for each
worker:

Sort Method: external merge Disk: 4920kB
Worker 0: Sort Method: external merge Disk: 5880kB
Worker 1: Sort Method: external merge Disk: 5920kB
Buffers: shared hit=682 read=10188, temp read=1415 written=2101
Worker 0: actual time=130.058..130.324 rows=1324 loops=1
Buffers: shared hit=337 read=3489, temp read=505 written=739
Worker 1: actual time=130.273..130.512 rows=1297 loops=1
Buffers: shared hit=345 read=3507, temp read=505 written=744

Is this a bug?