The partial fillup checkbox on Fuelly Mobile stopped working recently. I've tried it on Android 2.3 and Android 4.0, and it doesn't seem to have an effect on either. (It was working on Android 2.3 until a month or so ago.)
I just added a test fuel-up from Android 2.3 from Fuelly Mobile, I checked partial, and the fuel-up showed up as a partial in my fuel-up log. I was using the default Android browser and the standard (not Basic) mobile site. So it's checking out ok for me, at least.
When you said the partial checkbox has no effect, can you describe that a bit more? Your fuel-up wasn't marked as a partial?