if the bug say so, you must decide which information you wil trust. And all i know is that:
a) the original bug dont prevent a system from booting (not tested with wireless systems)
b) the patch in .4 is only about the upstart scripts, which will return 0 if no upstart is installed.
So i would say: It is safe to update. if your system dont boot after update this is not the fault of ifupdown. Then there are other problems. But this is only my opinion for these bugs ...
But there is a big chance that i be wrong. I don't know much about linux, esp, inits and networking. :twisted: