Ran into an issue that seems illogical to me, did anyone else experience this?

I managed to reach 100% dweller happiness and worked on keeping that level up. However, since yesterday my global dweller happiness rating is only 99% (on the main screen), and the weird thing is that when I list my dwellers, everyone has 100% happiness.

So either there is a round-up round-down problem with the global rating calculation, or something does not display correctly.

Any ideas anyone?