In custom editor window, label text in child windows sometimes becomes blurry

Hi,

I have a custom EditorWindow. In OnGUI(), I draw child windows with GUI.Window() between EditorWindow.BeginWindows() / EndWindows(). Each windows has a delegate GUI.WindowFunction in which I only do simple GUILayout.Label(), no GUI custom style.

In Unity 5.1.4f1, the label text stays sharp / normal. But starting with Unity 5.2.0f3 up to latest (5.3.2p4 & 5.3.3p1), on displaying a new child window, the text is first sharp, then the text gets blurry after some time.

No idea what exactly triggers this change in the editor. This doesn't reset when exiting / restarting the editor or reseting the Unity Editor layout.

I tried GUI.Label() just in case, but still blurry.

I am switching display between several groups of child windows, for each group of child windows only position are stored in an asset, and reimporting doesn't change a thing.

I'm using the "child window index in group" as windows id, so I am actually re-using / recycling windows id when switching display to a different group of child windows. I tried offseting the windows id, but it doesn't seem to make any change.

Just in case, I tried switching to DX9 instead of DX11 using -force-d3d9 command argument, but doesn't change anything.

This is on Unity 5.1.4f1

This is on Unity 5.2.0f3 up to 5.3.3p1

Was there any GUI system change in 5.2 that can explain this? What should I do?

Or is it a bug? (could not find any related bug in Unity 3d issue tracker)

Thanks!

Maxime