QC disappears and reappears when first switching to (Qml) Design

Steps to reproduce:

• start QC with QmlDesigner plugin enabled and empty settings, e.g. using the parameters "-tcs -load QmlDesigner".
• create simple quick app from template
• open the qml file
• switch to Design mode

Current behaviour:

• QC disappears for a split of a second and re-appears with the Design mode
• follow-up switches are okay and happen without disappearing

Expected behaviour:

• all mode switches happen without disappearing

I suspect some QtQuick Widgets or ADS issue?