I completely understood all John's suggestions and I already use them (creating false rectangles for example as I initially said). I've tried to avoid using layers and that is something that maybe I'll have to try again. Since moving from bitmap to vector apps that I haven't used them (except for Xara's flash to create animations and even a step by step tutorial).
For my day by day work I thrive to make things simple (for my taste and design process), but sometimes it isn't possible.
This isn't really a bug, just a canvas size limitation that I don't know if it would require many coding changes or why it exists in the first place (it must have a reason I guess).