If a Shape contains multiple ShapePaths, and one or more of them are given transparent stroke and fill so they become invisible, then when they are made visible again, their place in the z order is sometimes changed. This can be seen like this (in current dev):

qml tests/baseline/scenegraph/data/shape/shape_order.qml

This does not happen with the software backend, and it was recently fixed in the curve backend (ref linked issue).