Errr, this only uses a single FileBrowserSheet (I call close(), immediately after the open()).
The problem is intermittent (I think it's a race condition, from looking at the code populating the directory listing is done by a separate task.).
What the sample does is:
a) Create a new FileBrowserSheet.
b) Set the root directory to the current working directory. (Anywhere that's not user.home is sufficient.)
c) Set a disabled file filter that will break out of the loop, and raise a error, break the loop, if it sees files not in the current working directory.
d) Opens and closes the FileBrowserSheet.
I'm not sure if this is the best way to demonstrate it, but what happens in my app (or if I open a FileBrowserSheet) is that once in a while, despite calling setRootDirectory(<Somewhere other than user.home>), the directory listing contains files from my ~ in addition to files from <Somewhere other than user.home>. More rarely, I see "all files are from the correct directory, but everything is duplicated" (Eg: ~/tmp/foo.xml is listed twice).
Even if I don't use a loop here, and just have a simple app with a button that opens a FileBrowserSheet after a setRootDirectory(somewhereElse) call, I can get the problem to appear eventually with enough manual clicking. But since that is tedious and annoying, I used a loop and a automated way to detect that something anomalous has happened.