Recently I was not able to find a supermarket by it's name using my favourite navigation application Here from Nokia (I wrote about it already). I was in the place with very bad internet signal. I had all maps offline and expected that the only data Here reads from the internet is traffic.
Nevertheless, it failed to find a place until I found better connection.
Offline/online logic of Here was not very clear to me, therefore I explicitly turn offline mode ON in the application and searched same supermarket again. And it found it immediately.
So, when offline mode is NOT forced in the application it still tries to go online for data even if offline maps are available and even if internet connection fails (it could try offline in this case). At least it looks like this.
short story very short: it is not enough to download maps for offline usage, you should force offline mode in the application settings.