SVN 9260: There is still a major exploit with SM: Usually when you select a Quality promotion you lose all of your experience points, but when you have a unit that
lost promotions (due to upgrading) and select a Quality promotion to replace it, you don't lose any experience. In fact, it is easily possible (as I have seen with my current game) that you can select several Quality promotions at once.
I upgraded a slinger to an archer, lost 5 promotions IIRC, and then I could select 3 Quality promos and 2 star promos to replace it. I ended up with an archer unit with a str of around 23 (elite + 2

), in early Ancient. Of course, after that, the exp points were gone, but that unit will be able to compete for quite some time.
Unfortunately, I don't have a savegame to replay that issue quickly, but I seem to remember that this exploit has been valid for quite some time.
Would it be possible to offer a Quality promo only when it's possible to erase the experience of the unit - which doesn't seem to be the case when you are in the process of replacing lost promos?