unknown -webkit selectors being deleted

[gastrodon]

After combing, unknown -webkit selectors are being removed, with no visible way of changing this behavior

for instance

#editor {
  flex-grow  : 1;
  order      : 2;
  color: #ffffff;
  background: #00152d;
  -webkit-user-select: none;
  -webkit-app-region: drag;
}

becomes

#editor {
  flex-grow  : 1;
  order      : 2;
  color: #ffffff;
  background: #00152d;
}

[Bazowsky]

Same for other "unknown" properties.
Like a

html {scroll-behavior: smooth;}
h1::first-letter, h2::first-letter, h3::first-letter, h4::first-letter {
color: #f72377;
}

becomes

html {}

h1::first-letter,
h2::first-letter,
h3::first-letter,
h4::first-letter {
  color : #f72377;
}

Last commits on Oct 26, 2017, seems there is no way to resolve problem by author.