Unable create a new branch if the name ends with an exclaimation mark(Mac)

[namia]

I tried to create a new branch with a name that has an exclamation mark(!) at the end. Sourcetree will tell me this is an invalid branch name. 

If I try to checkout a branch with an exclamation mark at the end, sourcetree does not let me and displays a "invalid remote branch" message.

Trying the same on a Windows machine works.

I don't believe the exclamation mark is an invalid character for branch names according to the git documentation.

I'm using the lastest build on Mac 4.1.6(242)