Tempo Markers Being Tricky?

Hi there,
I am arranging a piece based off sheet music. I copied the sheet music directly into Musescore and played it through, it worked perfectly. I saved this, then started a new file with the same music, where I added 8 bars at the start of the piece to change the intro slightly (thus making all the music shift left by 8 bars). My issue is, now all of my navigational markers (D.S. al coda and "To Coda") have dissapeared and are not functioning, as has a tempo marker I had at the end of the piece. BUT unlike the navigational markers, which are completely absent, I am getting a random tempo slowing at the end of the piece (even though I can't see any tempo marker). However, the tempo slowing is occuring too early, it's as if the tempo marker pinned itself to a specific part of my piece, then when I added the 8 bars at the start it refused to move with the music and just dissapeared instead.

What I want, is for my navigational markers and tempo sign to stay pinned the the music I place them on, as opposed a specific bar. Is this possible? Or is there maybe some other way around this problem? It would be great if there was, I guess my only other alternative would be having to wait until I've finished arranging the whole piece before putting markers in.

Hopefully I've explained that okay, I've attatched both files mentioned above. Any help would be great!
Also, please note that I'm nowhere near finishing the arrangement yet, so that's why the intro sounds horrible! :)
Thanks