Problem with Nanowii?

[neilma]

Hi folks,
I';ve recently built up a Flyduino Nanoquad with the Nanowii as the controller.
If I put it normal mode it flys very well (too well for my limited skills  ) on the standard PIDs and settings.
However my issue is that if I put it into Horizon mode (or level) it will fly fine for a few moments (15 secs or so) and then it will start to pitch forward meaning I have to pull back slightly to keep it hovering. Sometimes if I switch back out into normal and back again, its ok, other times it stays like this.

Any ideas what could be causing it? Faulty ACC? (It calibrates fine and level).
I';m using Multiwii 2.2, Turnigy Plush 6a ESCs (ive flashed to BLheli but the problem occurred before flashing too) and Turnigy 1811 2900Kv motors + Nanotech 950 2s Batteries (oh and a Turnigy 9x with Orange satellite)

Also - is there a difference between Level mode and horizon mode?

[neilma]

So, as an update to this - The weather was nice today so took the quad outside and all seems to be ok. Not sure its a problem flying this one indoors, but outside it performed great!