Comment 7 for bug 900861

Serge (sboivin), you're being rude and that's not an good way to have others fix things for you, for free.
The reasons this has not been fixed for ages have been explained elsewhere: to sum it up, it would break too many modules. No capitalist-from-hell logic at work here.
Actually the R&D team is working to a generic solution to this bug: making sure the context is passed implicitly. That should land in v7.0 according to the roadmap. Let's bear with them.
In the meantime, you can try Gustavo Adrian Marino (gamarino)'s patch and report here, or browse the user's language to make up a context in your own on_change function.
Lionel.