This is something I've noticed in all of my recent Debian based distros (Debian 8, Mint 17, Ubuntu Trusty). If I run XTerm, I can get to the left mouse button menu (ctrl-leftmousebutton) which is "Main Options", the right mouse button menu (ctrl-rightmousebutton) which is "VT Fonts", but the center mouse button menu (ctrl-middlemousebutton) which is "VT Options" no longer shows.

If I ctrl-click the middle mouse button rapidly a menu outline flickers, but never shows. I do notice that the content scrolls if I move the mouse up and down.

I looked around at various .Xresources and .Xdefaults and did a search through /etc to find out if this has been remapped somehow, but I wasn't able to find any mention of Btn3 or Middlebutton being remapped for XTerm* resources.

Are you using a real 3-button mouse or a builtin mouse ?

I noticed that also on my T420 and wonder if it was a change due to something in a newer version of X or the kernel mouse device. BTW, that would work in fvwm but now it does not.

Anyway, you can enable 3-button emulation to get a work-around

John

It's built-in to a Lenovo pointing stick keyboard.

I'll try enabling 3-button emulation at some point.