How to change the resolution on a X or Y axis witouth having a scaling issue? How to change the resolution on a X or Y axis witouth having this weird scaling issue ?

for example, when searching a good ratio for a shot, you want to play and start changing the ratio of the rectangle of the shot as you wish , but blender after a certain point, (after hitting a 1:1 ratio ?), completely change the XY relations, i really dont understadn why, he start cropping the image on the other axis for some reasons... is this a bug ? i find this really annoying ... if anyone know a way to stop this behavior, either by tweaking a setting that i dont know (i tried tweaking aspect XY but same problem)with a add on, or a custom script somewhere ? please tell me 


in this gif i only tweak the x resolution but somehow, blender re-crop on the Y axis

thanks
The apparent inconsistency is due to the camera Sensor Size being set to 'Auto'.

When set as 'Auto', Blender will use the specified sensor Size as the size of the longest edge of the sensor - and in your example this will correspond to the largest of the X and Y resolution. This means that whichever dimension is the largest will dictate the effective size of the sensor and this (in conjunction with the Focal Length) determines the view from the camera - hence the change in behaviour when the X dimension crosses the threshold of the Y dimension in your example.

The solution is to change the Sensor settings to Horizontal or Vertical. This locks the 'Size' to correspond to that specific axis.