You do realize that working on Maemo 6 means bring Maemo 5 forward, do you?
It's not a new entity.

Bugs files for Maemo 5 will likely be fixed into Maemo 6 as well as it's a evolution of Maemo 5.
What will change will be the UI, based on Qt and with new interaction and new widgets... but the core is based on Maemo 5 with all the fixes.