Grids certainly can be a challenge but for anyone to assist you, the forum needs a sample of your plight up on apex.oracle.com. Knowing the theme is part of the solution but seeing how your region and grids are established needs to seen.
Something else to consider, take a look at the Packaged Application, Sample Forms and Grid Layout. It may be of some help.
thanks for your reply.
As you can see in my attached screenshot the problem are the items with type of Select List. At rendering time the APEX engine doesn't know the greatest length of the according LOV values.
I think that is a problem of the theme 25. What effective workaround does exist?