Cannot type right curly brace in VIM
While checking the questions from @arcdale's comment, I found that &lt;ALT-9&gt; does not produce a } on the commandline, too. The cause of this was simply that I had mapped the navigation shortcut to switch panes in iTerm  to &lt;ALT-Number&gt;. Hence, binding switching panes to another combo solved the problem.

Howvever, this does not explain why there was a problem with &lt;ALT-9&gt;, while all the other combinations, &lt;ALT-5&gt; to &lt;ALT-8&gt;, worked as expected.