portage-2.1_pre3-r1 doesn't set the title of mrxvt - works ok on xterm. Attached patch fixes this, works ok on xterm too. .bashrc uses \033]0 to set the terminal title also.
Created attachment 76025 [details, diff] portage-2.1-pre3-r1-output.py-mrxvt.patch
fixed in rev 3306, thanks for the patch
This has been released in 2.1_pre10-r3.