After chatting with suv on the jabber chat room (very helpful & friendly, thanks to him !).
It turned out :
- the document containing a complex pattern IS ACTUALLY PROPERLY exported. The blank display + crash was due to the Linux "evince" reader, thus, due to libpoppler I guess. I installed Acrobat Reader 9 (from the Ubuntu Partner repository) and... rendering is perfect !!
- there's a HUGE memory leak. Just zooming in and out a document containing 1 object with the aforementioned pattern literally eats HUNDREDS of Megabytes per second !
I would also definitely be willing to contribute to the Inkscape fund. It seems that ATM the Gimp team is considering to use their donations for bounties. But bounties for tasks that wouldn't be performed otherwise : annoying but required stuff, like optimizing etc. If you launched such a campaign on your website, considering the high number of users, it could be successful. I would definitely be willing to contribute through a recurring payment option.
Cheers