I thought I'd post this to help others who may run into the problem. (And use the forum search facility ;-) )

I've been having some display problems when print preview turned on.
It turns out it is a bug BUT there is an easy solution for those experiencing it.
Here is the reply I got from tech support:

"it seems to be an issue with caching. Disabling cache groups and
layers from Utilities\options\tune-ups and this will prevent the
problem from occuring."

This works perfectly and many thanks to Xara tech support for the speedy solution.