Switching git branches loses files until I restart PHPStorm

Hi.

say I have two identical git branches, branch1 and branch2 

I add a new file in branch2.

Add it to git, Commit it and then checkout branch1

the new file is not there which makes sense as it doesn't yet exist in branch1

if I then checkout straight back to branch2. No amount of synchronising or waiting will make the new file appear in branch2 until I restart PHPStorm.

I create the file in PHPStorm and switch branches using the terminal within the IDE.

I am running PHPStorm 2018.1 on OSX 10.14 I have experienced the same issue on the previous OS.

Is their I setting or workaround I can do to avoid restarting every time.

Thanks

Toby