So yeah I was just scrolling through my show room when I realized that I needed to upgrade it. I did a few several times and then I realized I didn't have enough TU, But I click the upgrade button anyways. Guess what happened. I had a negative amount of TU. So in other words I can upgrade 100 billion  times Even with no tu. But the consequence was that you had a negative amount of TU.  I don't know if it's on glitch or not,  But I would like it to be fixed. 

This has already been an issue pointed out before. We already have placed this on the list of fixes to be done so hopefully it gets fixed really soon.