The global linetype scale is not logically connected to the drawing unit.
Basically, line patterns are made for printouts and defined to look good on paper. In the print preview and for printing, the global linetype scale should almost always be 1 or very close to 1, independent of the drawing unit or the drawing scale.
For example a dashed line with a line weight of 1mm is always rendered with 12mm dashes and 6mm gaps if the global linetype scale is 1.
In model space, there is no paper size, drawing scale, etc, so it is simply not possible for QCAD to know how the line patterns should be displayed. I understand that this is inconvenient, but I haven't found a solution yet which is completely satisfactory and compatible with other products.
One possibility would be to view the screen as 'paper' in model space and display line type patterns to look good on the screen. This would mean that dashes would have a constant size in model space and not increase when zooming in (like in QCAD 2). However, this is relatively costly since dashes have to be recalculated whenever the zoom level changes. It also makes line patterns unpredictable in model space (a text might be placed in the drawing so it does not overlap with the dashes of a dashed line - this is not possible if dashes are constant and independent of the zoom level).