Thanks for the encouragement Doug, I am amazed at the discussion that my topic has generated. The information I have found out in the last couple of days is immense:-
Wet capping and dry capping,
Convex and concave capping,
The bees extending the flow frame plastic cell sides further out with wax before capping,
Flow frames need to be fully capped before splitting,
The moisture content of the honey being affected by the prevailing humidity,
Even that the moisture content of the honey in capped cells can be higher than in the honey in uncapped cells in the same frame,
The reassuring feedback that many people have had the same problem, also reassuring that the majority of people with flow frames do not have this problem.
As I mentioned in an earlier post, I think my problem is my colony is not strong enough. They have a langstroth honey super which they use quite normally, and they seem not to need the flow super for storage but maybe use it as an area for curing their honey. My solution could be to remove the langstroth honey super and then they would have no choice but to use the flow super.
Thank you to all, for your welcome suggestions and knowledge. Tom.