iTerm2: Option + Number (0..9) key not working

I have a German keyboard layout and need e.g. Option+7 to write a pipe (|). Option+Letter (Letter=a..z) works fine, but Option+Number (Number=0..9) is not producing anything. However, if I press Option+n (~) and then Option+7, surprisingly I get ~|. This behavior is only in iTerm2. The setting in *Profiles >> Keys* is Left option key acts as Normal and Right option key acts as Normal.