How to eliminate deprecation warnings when saving in Glade?

Question

Each time I save a project in Glade, I get the message Project "project.ui" has errors. Save anyway? I can't seem to find a way to resolve this issue.

I checked the following:

• Glade version is 3.38.2
• The target is set to Gtk 3.24
• Installed Gtk lib is 3.24.34
• As an example, one of the widgets gets complaint: [MainWindow > GtkBox > GtkGrid > GtkGrid > mainwin_chart_z0_cbtext] Property 'Double Buffered' of object class 'Widget' is deprecated. I didn't change the default property, and even checked the .ui file and it doesn't mention Double Buffered in that widget's XML.
• Same happens with Property 'Margin on Left' of object class 'Widget' is deprecated and several other properties.

So, why do I get the complaint in the first place, and how do I eliminate this?