It also doesn't seem to know its left from its right sometimes - again inconsistent. "Your destination is on your left" when it is on your right - and its not just Fleet services.
That one does seem likely to be map inaccuracy - discrepancy between where the destination has been resolved to by Google and where the on-board map thinks the road actually is. My experience seems to be that it's consistent (right or wrong) for a given destination.
The roundabout one doesn't seem to be the map as such - usually the map display shows the exits perfectly, just inconsistent with what the voice was saying. At some roundabouts it has a reasonable excuse, as it's ambiguous whether it should count "exits" that you can't turn into - obvious ones like exit slip-roads that are no-entry, or less obvious ones like laybys, farm tracks, weighbridges etc that are accessed from the roundabout but not really roads. However, I've recently have it give the wrong number on completely standard crossroad style roundabouts where there's no possible ambiguity.
Possibly the map data has labeling on the exits to fix the ambiguous case and the errors are where it is mis-labelled? Or else the voice direction just has bugs in interpreting the map.
The third category of unheplful directions is "not a bug" - the ones where it says "bear left", which make sense if you start thinking of it as meaning "don't accidentally turn right". Most cases of "bear left"/"bear right" actually need you to go roughly straight on and the message is just to warn you not to get in a lane for a turn into a relatively major diverging route. Entry into Cambridge from the M11/A10 is a classic case - there's a set of traffic lights with a major right turn for the road going to the hospital and a slip road slightly left of straight for going into the park-and-ride. If you are heading straight on, the nav will tell you to "bear left" to avoid taking the right turn to the hospital (which you weren't likely to take accidentally as it's a 90-degree turn), and taken literally that will cause you to end up in the park-and-ride which is just the sort of turn that in normal english someone would tell you to "bear left" into.
Actually, I've come to treat all voice directions simply to mean "now would be a good time to look at the map display", as that almost always makes the actual manoeuvre clear.
