subtle

Generally, this happens, when a program needs a specific aspect ratio and subtle sets a gravity that violates this. Windows can tell the window manager about this kind of preferences via their size hints and subtle can honor those.

There are two possible ways:

1. Enable size hints globally with the :resize option
   

   Numbers: on /off1 set :resize, true

2. Enable this per program via tag
   

   Numbers: on /off1 tag "name" do
   2   match  "name" 
   3   resize true
   4 end

Note: This can happen with Java too, see here for more information.