[LAU] RFV: LV2 Gtk2 UIs crashing Qt5 QTractor and MusE at same place

[Tim E. Real]

Hi list. Requesting verification of a bug:

After upgrading from *buntu 14.04 LTS to 16.x, the LV2 Gtk2 UIs 
 such as Calf and others crash upon opening them in both 
 Qt5 QTractor and Qt5 MusE-3, at these similar calls:

QTractor: In qtractorLv2Plugin.cpp
QWidget *pQtContainer = QWidget::createWindowContainer(pQtWindow, pQtWidget);

MusE: In lv2host.cpp:
ewWin = QWidget::createWindowContainer(x11QtWindow);

The crash ultimately happens deep inside the Qt5 libraries at the 
 same place in both apps :

	QXcbWindow::setParent()

I tried building Calf from source release, and tried different
 video cards. NG.

But... If I bypass createWindowContainer() in MusE the UIs open and work fine! 
(Just that now of course they are outside of the container window.)

It's Qt 5.5.1
I read about a bug fix and revert where they assumed always a valid screen 
 but then had to revert, but that's supposed to be fixed now.
I'm confused.

Is it just me getting these crashes?

Thanks.
Tim.