Darktable tethering and "live view": problems with zoom

I am a new user of darktable. I have version 2.4.4., running on Linux Ubuntu 16.04. My camera is a Canon EOS T6 Rebel. I use tethering and live view. It is important that I can focus via tethering, and the basics seem to work well, but there is one problem: The zoom function (icon “zoom live view” or shortcut “z”) always zooms to 100% (in 2 phases: for a second or so, a weaker zoom appears, then the 100% zoom appears, as if I had pressed the key twice in rapid succession). This is not good, since I often want 50% zoom.
The problem occurs whether I use the “z” key (keypoard input) or the icon (mouse input).
Is this a known problem? Any workaround?