Plan view in Web Client - Wrong Categories hierarchy display

Hello,

I am evaluating RTC v3.0.1 and I have found the following "strange" behaviour.
My project has a root Category and 3 child categories:

Unassigned (root)

Cat1
Cat2
Cat3

I have created a Plan view "By Category" that displays the work items in a tree and grouped by category.
To my surprise, I have observed different behaviour of the "By Category" view if I open it with the RTC Eclipse client or if I use the Web Client.
The difference is that while the RTC Eclipse client does show the Category tree as expected (with one root node and 3 children), the Web Client surprisingly shows something like this:

Cat1
Unassigned(root)

Cat2
Cat3

with Cat1 being at the same level as the root parent category, which is wrong.
Is this a known bug? I can not understand the reason for this inconsistency otherwise,

regards,