I appear to have found a work-around. I was informed by Google some time ago that my googlemail account was going to be replaced with a gmail account, I don't know how relevant that is, but I had a feeling this problem had something to do with syncing, so I checked out the google accounts I had listed on the phone, there were three; my wife's (so we can share a calendar), my googlemail and my gmail accounts - I can't remember if I put the gmail account on there manually or not when I set the phone up, but it seemed pretty pointless to me so I just deleted the gmail account from the phone and rebooted it. That was about a week ago and I haven't had this problem since.
In the absence of anything resembling a contact path for Google I emailed Samsung and received a pretty good response and they did offer some advice and a process to follow, but they seemed to be working on the assumption that it was an update that had caused the problem, when in fact the problem had been in evidence before the phone had an upgrade.
For information, their response is below:
Thank you for contacting Samsung.
I’m sorry you are having issues with the Contacts app your device. I can understand your frustration about this as this should not be happening.
Old systems settings can be left on the phone after an update occurs, which is why we usually recommend a full factory reset after updating. If this isn’t done your device may begin to give false readings from system resources, or experience technical problems, which may explain the issue you are having.
We would advise on doing the following, which is designed to reset the settings on your device. Please back up your device using Samsung KIES before you do this.
1) Remove the battery for at least 40 minutes, put the battery back in and allow it to fully discharge. Afterwards, perform a full battery charge with the device turned off. Do not interrupt the charging process.
2) After the battery is fully charged, we would like you to perform a full factory reset, which can be done via Settings > Backup > Reset.
This process will reset your device, remove old system files that are no longer needed and enable your device to operate normally again.
Please let us know if your device continues to experience problems after the reset so we can investigate further