[el-Odysseas]

I guess reloading the song would set the metronome to the song-tempo and not the last tempo set in the metronome.

I would not have any problem with this eather

I understand, that you expect the metronome settings/edits to be "remembered"/ saved. Everyone has his own workflow!
For me is not important for the metronome-tempo to be saved,  since I change it constantly while practicing: from 50 BPM, to 60 BPM, until I reach the song-tempo. 
The song-tempo on the other hand is a part of the song, like it's title/notes/character etc. and cannot be changed.
So my problem is that whenever I practice and use the metronome the song-tempo also changes. The next time I load the file, I do not remember the exact "target-tempo"/ song-tempo.
It is maybe a bad analogy, but imagine after practicing the half of the song, only the half of the song-title is being saved.

Maybe another possibility could be that the metronome edits are being saved, but in edit mode there is a distiction (2 Tempo-fields for example) between metronome-tempo and song-tempo.