Our application needs to use the inactivity timer to find out how long it has been since there has been activity, but this is made extremely difficult by the following.

There are some system dialogue windows, for example :

"You have:
3 missed calls
1 new message"

The problems with such windows are :

1) they turn the backlight on when they become foreground
I think they should only do this once (ie when there is something new).
Our app is like a screensaver and so starts automatically. It uses a lot of
battery, so we kill it after 45 seconds. This makes the above system
dialogue window come to the foreground and thus the back light comes on.
This behaviour is very undesirable.
2) they turn the backlight on by resetting the inactivity timer.
Our app is a screensaver and so relies on the inactivity timer. Using the
inactivity timer to turn the backlight on is perverse, since the backlight
and inactivity timer are unrelated. Using it in this way makes the inactivity
timer close to useless for it's intended purpose (which, I'm sure, isn't to
turn the backlight on).

Please consider implementing a dedicated function to turn the backlight on, (that works on all phones), and using that instead. Also, please publish this functionality (wiki example?) so that 3rd parties can also stop using the inactivity timer in this fashion.