Memory leak when dynamically creating and deleting elements/materials/meshes in continuous loop

Creating and deleting elements, materials, and/or meshes dynamically in a loop causes application memory consumption to rise steadily, so there appears to be a memory leak somewhere.

Test application from https://codereview.qt-project.org/c/qt3dstudio/qt3dstudio/+/262538 can be used (click "Memory leak test" button and check task manager for increasing memory consumption).