Interpolate to the Medium version

Dear Glyphs,

Still working on my Regular and Bold, I was curious about interpolating to the Medium version. So, after reading the tree parts of the tutorial, I made a little test version. Most of the interpolation is fine.
But, see plate 1. My reg and bold fi ligature differ from each other and of course I was curious what the Medium would be in this case.
See plate 2. But now the program changed my Bold fi. That is not what I wanted or expected. I want to have the freedom to differ the Reg and Bold. But is interpolating possible in that case? And, is it possible to change the Medium by hand?
Thank you, Titus

Check the values in your instances, it looks like your Bold instance has different values than your Bold master.

Yes, my mistake. Thank you, I’ll test again.