I've been breaking my head over this. My application works fine until I add QwtPlot. It seems like QwtPlot likes to be 200x200 no matter what. Stretch factors don't seem to work with it, size hints don't seem to affect it, size policies have no effect... This widget is broken and I don't know how to fix it.

Here are some examples!

QwtPlot resizes as it pleases, disregarding layout constraints.

Open QtDesigner, add an MDI area, add two sub-windows and add two QwtPlots in each (with layouts, so everything resizes when stretching the window). When switching between the two tabs, the QwtPlot will decide to resize to 200x200 and push the other plot out of view:
https://youtu.be/pXkut7SwKxY

The same is true if you build this structure in code. The following video shows the same issue in my application:
https://youtu.be/-oMESWIeEhM


QwtPlot doesn't obey stretch factors (or it acts weirdly). This next video requires some explanation: I want the plot at the very bottom to have a fixed Y size. The other two plots at the top should scale evenly when the window is resized. This works fine when QwtPlot is not added to the layout. When I add QwtPlot, it no longer does what it should. Notice how the plot at the top actually stretches larger than the one in the middle. Why? Why is this happening?

https://youtu.be/MBIITNObzzg


Things I've tried

Setting row stretch factors does not fix the second issue. QwtPlot ignores these.
Setting the size policy to "Minimum" (or anything else for that matter) has no effect on QwtPlot. It doesn't care.
Manually calling resize() on the main window whenever a subwindow is activated doesn't help. QwtPlot will resize however it sees fit.

I'm out of ideas and would really appreciate some help here.