branches with a comma in it are happily created, but cannot be switched to

SourceTree happily created a branch for me having a comma in it:

feature/0001172__RESEARCH_foo,_bar

but checking out gives this error:

git -c diff.mnemonicprefix=false -c core.quotepath=false checkout feature/0001172__RESEARCH_foo
error: pathspec '0001172__RESEARCH_foo' did not match any file(s) known to git.