execute operation fails with one argument with spaces (wrong use of setNativeArgumenst)

We now have an installer which works fine on "slow" computers and fails on "fast" computers. The installer consists of two components, one of them obligatory and one optionally. See attached installscripts and package definitions. In total three other installers must be started during installation, .Net framework redistributable, a driver and MS Visual Studio component runtime. These are started with the installscripts. This works fine on a normal machine with Windows 7 64 bit installed. When trying to install on a fast computer with an SSD disk we run into the problem, that the other installers, that are triggered by the installscript can not be run. Seems like the function that starts the corresponding installers (in our case batch files) are called before all part of the component are unzipped!? See the image with the error message, the install log file and our installscripts.
Do you have any suggestions how we can fix this strange behaviour? I would also like to understand when exactly the functions in the installscripts are triggered.