Thank you for the explanation. I understand why certain stats could decrease during the training. I just think it would make more sense if they did not. Is that a limitation of the engine or a desing decision of Dioxine?
It needs to be that way to prevent abuse. For example, the cap on TU for gals is 100. You can get more than that however, because of the way statgain through missions work. If you are under the cap, you get statgains, if you are above, you do not. So if your gal has 99 TU and gets +3 from the mission, she will end up with 102 TU, but can gain no further. This overshoot is not too imbalanced, as statgains from missions are not that large.
When you consider MMA training however, you get a large increase to TU of +10. You have the option to cut that down to the cap of 100 or not. If you would not cut it, your 102 TU gal would get +10 TU and end up at 112. That would also mean to get the most out of it, you should not use MMA training before your gal is maxed.
Of these two options, to cut at the statcaps is clearly more balanced.