yeah that issue has been around since the unit size upgrade option was added to the game. it's been reported about a dozen times since then 
interestingly, the gildar cost has been changed twice since then (initially, it was 15g, then 30, now it's at 50g per figure).
perhaps there is an internal problem that makes it hard to implement the obvious solution. that seems unlikely, since the button is on the same screen as the weapon & armor upgrades for which the resource & gildar cost seem to work fine, but we don't know how the size upgrade is actually implemented, so it may not be as easy as one would think.
either way, it's probably not considered a game breaking problem, since there's no multiplayer and you can easily avoid using the exploit in single player.
