[Pharo-project] Confused about #isDirectory

Hi, I don't understand why '/tmp' asReference isDirectory. false '/private/tmp' asReference isDirectory. false '/Users/sven' asReference isDirectory. true '/Users/sven/Desktop' asReference isDirectory. true on Pharo 1.4 Mac OS X Cog VM. Anybody any idea ? Am I doing something wrong ? Thx, Sven