I just found a "solution" to the problem. I changed in the autocomplete code the function which reads the settings. options.matchSubset = options.matchSubset || 1; to options.matchSubset = 0;
I know this isn't a nice thing to do, but it works! Don't ask me why, but it does. If I did accidently override my settings somewhere in my code I'd understand why this helps. But I'm 100 % certain I don't do this. Maybe one of you guys can explain it, I can't, but I'm just happy it works. Thank you for trying to help and for creating this plugin!