Bug introduced in 11.3 or earlier and persisting through 12.1 or later. Fixed in 13.0.0 or earlier

I didn't expect any difference between these:

dsa = {{{#@{3}}}, {{#@{2, 2}}}} &[Developer`ToPackedArray];
dsa[[All, 1, 1, -1]] = q;

{{{{q}}}, {{{q, 2}}}}

asd = {{{#@{3}}}, {{#@{2, 2}}}} &[Identity];
asd[[All, 1, 1, -1]] = q;

{{{{q}}}, {{{2, q}}}}

What makes the differences?

Update: I reported it for version 12.0 and got a response confirming it is a bug.

  • 7
    $\begingroup$ Must be a bug in the implementation of write access to nestes packed arrays. The analogous read operations dsa[[All, 1, 1, -1]] are performed correctly in both cases. I would suggest to report it to Wolfram Support. $\endgroup$ Aug 27, 2018 at 15:23
  • $\begingroup$ Where is this difference coming from? What's the way to avoid it? This makes me nervous about my recent work's validity. Can we possibly find a work-around? $\endgroup$ Apr 19, 2019 at 19:35

1 Answer 1


The bug appears to have been fixed in V13.0.0 or earlier



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