background bottom strip

[step-]

When I load tabbedex and open a new urxvt client there is an inaccessible strip at the bottom of the window. In the picture of a very small terminal window you can see a red rod pointing at the darker bottom strip. The lighter grey area is as far as the working area goes, the darker bottom strip is inaccessible. The bottom strip remains when I resize the window, and when I open new tabs. If I don't load tabbedex or load tabbed instead of tabbedex, there is no bottom strip, everything looks OK. My settings:

URxvt.tabbed.new-button: false
URxvt.tabbed.autohide: true
URxvt.tabbed.reopen-on-close: no

I also tested autohide: false but the bottom strip is still there.