I tried this on my 3GS at different places. Some places, the bars dropped from 5 --> 0. Others it went from 5 --> 3. In some other places, it didn't drop at all

I tried this on my 3GS at different places. Some places, the bars dropped from 5 --> 0. Others it went from 5 --> 3. In some other places, it didn't drop at all. It's pretty random, but the effect is certainly repeatable at the same location.