[BUG] Strange behavior when plotting the same subplot multiple times in one layout

[fredcallaway]

Details

MWE:

f1 = plot([1,2])
f2 = plot([1,3])
plot(f1, f2, f1)

This specific case produce f1 and f2 just once each, on the diagonal. In more complex cases, we see highly irregular behavior. I think the simplest fix is to add a check for this case and throw an error, to save future users from the long and painful journey that brought me here.

Backends

This bug occurs on ( insert x below )

Backend	yes	no	untested
gr (default)	x
pyplot	x
plotly
plotlyjs
pgfplotsx
inspectdr

Versions

Julia Version 1.4.1
Commit 381693d3df* (2020-04-14 17:20 UTC)
Platform Info:
OS: macOS (x86_64-apple-darwin18.7.0)
CPU: Intel(R) Core(TM) i7-1068NG7 CPU @ 2.30GHz
WORD_SIZE: 64
LIBM: libopenlibm
LLVM: libLLVM-8.0.1 (ORCJIT, goldmont)

[DanielReedOcean]

Presumably, this StackOverflow question is another example of the same issue.

[BeastyBlacksmith]

I can't reproduce this on Plots v1.27.4