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In version 10.1 I found a strange Plot behavior I did not anticipate. It seems that various heads including PlusMinus are treated as wrappers and stripped by Plot in a way that is not safe. This means that definitions that do not appear in the plot expression can radically and errantly affect its output:

ClearAll[PlusMinus]
Plot[x^2, {x, -1, 1}]

enter image description here

PlusMinus = Power;
Plot[x^2, {x, -1, 1}]

enter image description here

Surely this is a bug? What versions are affected? What is the easiest way to patch this in version 10.1?

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    $\begingroup$ v9.0.1 is not affected: i.stack.imgur.com/IpBYU.png. Persisting through v12.1. (Tested on Wolfram cloud. ) $\endgroup$ – xzczd May 22 '20 at 10:50
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    $\begingroup$ I think this may be the function that needs leak-proofing: Charting`ParserDump`plotStripWrappers $\endgroup$ – Mr.Wizard May 22 '20 at 10:58
  • $\begingroup$ Bug also present in v11.2. $\endgroup$ – Hans Olo May 22 '20 at 11:06
  • $\begingroup$ Further check shows Charting`ParserDump` context doesn't seem to exist in v9.0.1. $\endgroup$ – xzczd May 22 '20 at 11:09
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It appears that PlusMinus is the only wrapper that is not Protected:

Charting`PlotParser; (* preload *)

Select[Charting`ParserDump`$pAllWrappers, FreeQ[Protected]@*Attributes]

{PlusMinus}

We can remove it from that list to correct this bug, but perhaps induce others:

Charting`PlotParser; (* preload; do not remove! *)

With[{ov := OwnValues @ Charting`ParserDump`$pAllWrappers},
  ov = DeleteCases[ov, HoldPattern[PlusMinus], {3}];
]
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