shadow build changing original source location

This seems to be a recurring issue, given that Qt is supporting shadow builds (http://doc.qt.io/qt-5/configure-options.html), I'd like to verify whether this would/should include the 'promise' that nothing in the original source location gets changed/added...?

I appreciate this (making sure nothing gets changed) being difficult to maintain.

With 5.9.0-rc I've noticed for example:

• android builds add stuff like qtpurchasing/src/android/src/com/android/vending/billing: IInAppBillingService.java
• linux qtwebengine/src/3rdparty/chromium builds add their collection of *.pyc files

The main issue with changing stuff at the original location is that it can cause (at first sight) 'weird' issues with subsequent shadow builds for different platforms/archs.