Additionnal Bug ?

While playing with my test I found what seems to be a bug

The test files are :

xul link : http://tharbad.ath.cx/rdf/test.xul
txt link : http://tharbad.ath.cx/rdf/test.xul.txt
(is actually a symlink to http://tharbad.ath.cx/rdf/test.xul)
rdf source link : http://tharbad.ath.cx/rdf/test.rdf

The walkthrough is :

1 - load http://tharbad.ath.cx/rdf/test.xul in firefox
2 - click once to open the "Class" folder.

Notice that there's one element "Datatype" that is drawn with a folder 
icon, that let you try to open it.

3 - click once to open the "Datatype" folder.

Datatype is empty. So only the opened folder icon let you see that 
you've opened the folder.

4 - click once to close "Class" folder.
5 - click once to reopen "Class" folder.

BUG : Datatype is now no more a folder according to firefox presentation.

The only way to make it reappaer (without reloading) is to double click 
on the "Datatype" icon as it was a folder.

Optionnal :
6 - double click "Datatype" icon (nothing seems to happen)
7 - click once to close "Class" folder
8 - click once to reopen "Class" folder

SHAZAM !! : Datatype is now a folder again !

Is it doing this on all plateform or only on my firefox ? Is it 
concidered a "bug" ?

Valentin