Mouse context menu doesn't exists using pdfviewer plugin in webengine

• installed via online installer, some time ago a 5.12.x; now added next version 5.13.2
• start 'quicknanobrowser' application from examples
• load some pdf from internet
• everything is rendered fine butl right-mouse-button click doesn't work on whole window;
• select some text, this is OK, then right mouse click but no context menu
• context menu works only on pdfviewer menubar on top and maybe 10-20 milimetters bellow this menubar.

On Windows a shown small 1x1 milimeter rectangle is show on point of click