Within Terminal, `date` command outputs a curious prefix where it should'n
The issue was due to a bug in oh-my-zsh:


The bug was fixed several months ago: update oh-my-zsh and the issue should be solved.
If for any reason you cannot update there is fix on StackOverflow (https://stackoverflow.com/questions/12321564/date-command-with-zsh) but it involves the editing of lib/termsupport.zsh: remove the 12th line (warning I do not have oh-my-zsh installed and cannot check if the line number is really the correct one).