I have run Cygwin on multiple versions of Windows including recently on
Windows XP and don't think I ever had this problem. Resizing or
specifying a geometry always resulted in the exact number of columns
requested, with increments of 1 column being available when dragging the
borders of a window to resize.

Now, after upgrading to Windows 7 64-bit, I cannot get the window to
have 80 columns on resize. It jumps in increments of two or three,
depending on the number of columns prior to resizing. For example:

$ tput cols 
66 

xx50283@PP75W9D0R1 ~ 
$ tput cols 
69 

xx50283@PP75W9D0R1 ~ 
$ tput cols 
71 

xx50283@PP75W9D0R1 ~ 
$ tput cols 
73 

xx50283@PP75W9D0R1 ~ 
$ tput cols 
75 

xx50283@PP75W9D0R1 ~ 
$ tput cols 
77 

xx50283@PP75W9D0R1 ~ 
$ tput cols 
79 

xx50283@PP75W9D0R1 ~ 
$ tput cols 
82 

xx50283@PP75W9D0R1 ~ 
$ tput cols 
84 


Each one of those was queried after dragging the right-hand edge of the
window by the smallest it would change. I don't know if it is related,
but there is also several pixels (I would say around 20) gap between the
window manager border decoration and the parts of the display presented
by xterm. I did alter from the default Windows config for the desktop,
because I don't want the large default borders. I set "Border Padding"
to have a value of zero.

Should I be able to resize by increments of one column?

I have attached cygcheck output as requested in problem reporting
guidelines, and also /var/log/xwin/XWin.0.log files.
Thanks for any help.
Linus