Please ignore this thread, I'm just trying different options to see if I can pinpoint what is breaking the threads - I'll ask for it to be deleted once/if I find the root cause of the issue.
From what I have seen it seems to be after a picture is inserted into a rely - seen it happen twice now but other times it is OK.
I'll try different sizes and file types to see if there is any basis for this.
Thanks for your patience
Iain