SOT - car computer functions

I have a Jazz just over 4 years old. Like many modern cars, it can "sense" speed signs and show the limit on a dash display (this is /not/ the satnav display). If required, I can set the speed limiter to what the display says, and so keep to the speed limit. That's fine, but now and again I noticed the displayed speed would revert to the "pause" condition, where the speed sensor is awaiting a sign it can identify. That's not much use if the speed limiter is set, as in the pause condition it has no limit to conform to (it can revert to the previous speed limit after some time, even if still in the pause condition, but I have yet to find what that time is).

What was puzzling me was the apparently random nature of this pause condition appearing. I noticed it appeared at some roundabouts, but not others, where the speed limit displayed would just disappear. I wondered if it was chevrons at the roundabout or something else confusing the sensor. It was then I decided to RTFM, and it became clear (sort of...) what was going on. :

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The speed limitation function and warning function may switch to pause if there is no speed limit sign in the screen of the traffic sign recognition system when:

the end of speed limit or other designated limit is detected

your vehicle enters/exits motorway or highway

you make a turn with a turn signal to change direction at an intersection

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The first one makes some sense, the second less so, and the third no sense at all. Can anyone explain the reasoning behind this? Why should using an indicator at an intersection (and roundabout!) make the system assume the speed limit has changed or is no longer in force?

I guess it assumes that you are turning into a road with a potentially different speed limit, and it hasn't seen a sign to know what that limit is.

I have a similar system on my Hyundai Tucson (but without the option of automatically setting the speed limiter) - and that doesn't seem to know what the limit is, half the time. I also have a Tomtom stand-alone satnav which I use for speed camera warnings, and that usually has a better idea of the speed limit than the built-in system - but if the limit on a given road changes, it doesn't know about it until the next map update - if then!

One thing I've discovered about the speed limiter is that if you set the limit to (say) 40mph, it limits you to what the car's exaggerometer - sorry, speedometer - thinks is 40pmh, which is actually about 37. The Tomtom - but not the built-in navigation system - enables a suitable correction to be made.