Now I'm getting angry.
Look at the screenshot I posted at the start of the thread. In the unit list there is empty space at the right. This suggests that ***there are no more units*** after those shown. That is to say, that there are only five units.
Of course, that is not true. One has to use the buttons in order to see that there are more units available, "to the right".
My suggestion: use the empty space indicated by the question marks to display units, in other words so that seven, instead of five units, can be displayed at a time (I think two more unit graphics can be shown in the space available, which is where the question marks are). Keep the existing scroll buttons as they are, since obviously there will be many times when more than seven units will be available to buy or in the existing stack.
I hope I have been clearer. That screenshot should have spoken a thousand words. Alas... If it cannot be done or if it's not important, so be it. But many players will be confused. I can't wait for the many threads stating: "Why can I only build five types of units?" or "My stack had 14 units in it. Where did the other nine go?"
