My Tempo isn't working!

I am currently working on a detailed piece, but my tempo isn't working. As you will know, the automatic tempo for the palette is 80 bpm, and when i paste it into the document it is 80 bpm, but when I change it, musescore doesn't log it, it says 100 bpm, but when i checked in play panel it says 80 bpm. This is also confusing, because i have been working on my piece for a while, and it's only just started it!

Please help!