missing files after git merge
After some investigation I found the following. The file was added by me on master before creating the branch (that's why it was in my dev-branch). But now the crazy thing: The file was deleted in master afterwards by a colleague, but without any status information. Status log only shows the creation of the file. So the merge was correct, but due to the missing status information it was not comprehensible to me.
Check if there is nothing in stash
git stash pop
For new files, please make sure you add them first (git status should list them)
git add
The best docs about Git at all, including branches: http://git-scm.com/book/en/Git-Branching-Basic-Branching-and-Merging