join() not working as advertised

[rohintoncollins]

pubspec.yaml:

  path: ^1.9.0

join('/ZCLOUD', 'ZCloud Master Key :grinning:§ąśćżłóę:.txtÆ.txt')

should return

/ZCLOUD/ZCloud Master Key :grinning:§ąśćżłóę:.txtÆ.txt

It is incorrectly returning

ZCloud Master Key :grinning:§ąśćżłóę:.txtÆ.txt

Of note is the emoji 'colon-grinning-colon'
plus the other special characters '§ąśćżłóę'
plus a colon which is a forward slash in the macOS Finder file name (and is represented by a colon)
plus the 'Æ' character.