pg_restore V12 fails consistently against piped pg_dumps

When doing a parallel pg_restore (v12) against a dump created through a pipe using an earlier version (11 all the way to 9.6), it fails with the known error of not finding data offsets. I understand the reasons for it (potential inability to seek), which is documented in pg_restore. 

What I don't understand is why the same `pg_restore -j` worked in earlier versions (say running pg_restore_v11 against the same dumps). Has anything changed in terms of ordering? I am actually quite curious what led to this finally breaking consistently. 

I also timed things, and found that pg_restore_12 against a pg_dump_12 takes about the same time as pg_restore_11 vs pg_dump_11, on the same dataset. I initially did this to see if for some reason pg_restore_v11 was compensating for the lack of the offsets, but this didn't seem to be the case (or perhaps the dump is too small to matter, around 1.5GB).

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Wael