Pro Sites incompatibility with BBPress?

Hi

This topic is posted on 2 places :
- bbpress.org forum
- premium.wpmudev.org community support forum

While working on a site to be launched on the same day (= I had to have it working
I discovered something interesting

BBpress second level forum (= with a parent forum/category) also in the permalink, will result in page not found.
I searched for this issue and came across a few topics, where it was advised to reapply the permalinks, then save again the BBpress settings, where we set the slugs.
I tried everything there and still the same issue, but it was clearly an issue with rewrite.

So I begun to deactivate every other plugin I have and after every deactivation I tried if second level forums were loading. I thought specifically about security plugins such as Wordfence, Better WPSecurity, but nope.

Finally, it was when ******I deactivated wpmudev's Pro Sites plugin, that the second level forums were loading.*******

I tried another forum plugin but really I will need BBPress (big amount of subforums necessary on this website)

now I made some tests, and to make short :

- if Pro Sites activated :
-> 1st level forum will work
-> 2nd level forum will not work

- if Pro Sites is deactivated :
-> 1st level forum will work
-> 2nd level forum will work and can be reached with those 2 url
A: example.com/forums/forum/level1/level2
B: example.com/forums/forum/level2
(forums/forum beeing the slugs set in Forums settings page)

is it normal we can reach with 2 different permalinks?
***** and as it changes automatically, is there a way to force (in BBPress code) a subforum permalink to stay 1st level even if in a sublevel? would be interesting also in the case a forum is moved to another category then it wouldn't change url ***** (and at the same time it would solve/hide the issue with Pro Sites)

so cleary this is a rewrite stuff that goes beyond my knowledge, for info my permalinks are set to the second option /2012/06/07/exemple-article/ and .htaccess present with necessary change in it

I use also buddypress on that site but didn't go until desactivate it as it worked when I deactivated Pro Site,
the site I was working on has buddypress, but not the groups and forum elements checked, forum beeing BBpress anyway (I also tried to check/uncheck forums in buddypress settings, really not related to the issue)

so I was thinking to install a testsite with only vanilla WP Multisite and buddypress, as I need all my tests done that way
+ for this issue : Pro Sites and BBPress

so if there is anything you tell me to try, it will be done

thank you very much in advance (anybody, eveybody