BUG #17243: explain wtih recursive cte error?

The following bug has been logged on the website:

Bug reference:      17243
Logged by:          mark sloan
Email address:      mark.a.sloan@gmail.com
PostgreSQL version: 14.0
Operating system:   MacOS
Description:

Seeing a issue with 'EXPLAIN' throwing an error on a query that otherwise
runs without issue. 

example query case. 
---------------------------------------------
select x.v into explainctebug from (values('foo'),('bar'),('baz')) as
x(v);

query:

with recursive a as 
(
    select v, '' as x, 0 as n from explainctebug 
    union all
    select v, substring(v,n+1,1) as x, n+1 as n from a where n < length(v)
)
select x, count(*) from a where n > 0
group by x order by count(*) desc;


returns. 

 x | count 
---+-------
 a |     2
 b |     2
 o |     2
 r |     1
 z |     1
 f |     1
(6 rows)

--------

 EXPLAIN verbose with recursive a as 
(
    select v, '' as x, 0 as n from explainctebug 
    union all
    select v, substring(v,n+1,1) as x, n+1 as n from a where n < length(v)
)
select x, count(*) from a where n > 0
group by x order by count(*) desc ;


returns 

                                    QUERY PLAN
        
---------------------------------------------------------------------------------------
 Sort  (cost=5835.36..5835.86 rows=200 width=40)
   Output: a.x, (count(*))
   Sort Key: (count(*)) DESC
   CTE a
     ->  Recursive Union  (cost=0.00..4697.37 rows=46690 width=68)
           ->  Seq Scan on public.explainctebug  (cost=0.00..23.60 rows=1360
width=68)
                 Output: explainctebug.v, ''::text, 0
           ->  WorkTable Scan on a a_1  (cost=0.00..374.00 rows=4533
width=68)
                 Output: a_1.v, "substring"(a_1.v, (a_1.n + 1), 1), (a_1.n +
1)
                 Filter: (a_1.n < length(a_1.v))
   ->  HashAggregate  (cost=1128.34..1130.34 rows=200 width=40)
         Output: a.x, count(*)
         Group Key: a.x
         ->  CTE Scan on a  (cost=0.00..1050.52 rows=15563 width=32)
               Output: a.v, a.x, a.n
               Filter: (a.n > 0)
(16 rows)



EXPLAIN  with recursive a as 
(
    select v, '' as x, 0 as n from explainctebug 
    union all
    select v, substring(v,n+1,1) as x, n+1 as n from a where n < length(v)
)
select x, count(*) from a where n > 0
group by x order by count(*) desc ;

returns. 

ERROR:  could not find RecursiveUnion for WorkTableScan with wtParam 0



this seems like it might be a bug?

 PostgreSQL 14.0 on x86_64-apple-darwin20.6.0, compiled by Apple clang
version 13.0.0 (clang-1300.0.29.3), 64-bit