looks like a windows bug portability issue for me

  DB<54> x glob 'x{\{a\,b\}}y'
0  'x{a\\y'
1  'xb}y'
  DB<55> p "$^O, $]"
MSWin32, 5.024001
[download]

no such effect un linux or termux

  DB<1>  x glob 'x{\{a\,b\}}y'
0  'x{a,b}y'
  DB<2> p "$^O, $]"
linux, 5.018002
  DB<3>
[download]

> (if that's what you're referring to).

I was referring to the fact that quotemeta is meant for regexes, which have a differing set of meta-characters.

update

from File::Glob#NOTES

As a concession to user expectation, therefore, backslashes (under GLOB_QUOTE) only quote the glob metacharacters '[', ']', '{', '}', '-', '~' and backslash itself. All other backslashes are passed through unchanged.

OMG... oO