5.9: tst_qquickcanvasitem asserts when executed 2nd time/.qmlc files are present

Steps to reproduce:

• Run test once
• Run test 2nd time:

  Program: c:\dev\5-vs17-59\qt-59\qtbase\bin\Qt5Cored.dll
  Module: 5.9.2
  File: qml\qqmlpropertycache.cpp
  Line: 1188
  
  ASSERT: "properties.count() == propertyIndexCache.count()" in file qml\qqmlpropertycache.cpp, line 1188
  

• Remove all .qmlc files under data
• Run test again: works
• Run test again: crashes