I am sharing files with a colleague at the office over Bluetooth. We both have the same Mac, and are up to date with all software.
When he tries to look at a folder that contains files whose name contain an ampsersand sign, the folder just appears empty. It took some time to track that down, but we could eventually easily reproduce the behavior just by adding or removing the ampersand from a file name.
I could not find any reference to this issue describing it as normal, so, to me it's a bug.
Mac OS X Hints