Hello Kombrig,
What version of Composer are you using? Choose the About command in the Help menu. It should report Version 2.0 or Trial Version 2.0. If it reports something like Beta Version 1.9.16, or Version 2.0 RC1 (Release Candidate 1), then you might be seeing a bug related to a bug fixed that I reported at
www.notation.com/MidiNotateBetaRelease.htm for beta version 1.9.16.
I tried to reproduce the problem you reported for Enharm_Spell.not without success. I followed exactly the steps illustrated in my screen shots, except, as in your song, I made the second chord an eighth note duration instead of quarter note duration.
I don't doubt that you're seeing the problem you've reported. We just need to figure out what is different about what you're doing from what I'm doing.
Sincerely,
Mark