ERROR_VARIABLE from execute_process is not working as expected

Beginning from version 12, my CMake project is not working  as expected anymore. 

I have a CMake script file "myScript.cmake" that I run with execute_process, and then I parse the output, which results in a list of files: "myFile1.h;myFile1.cpp"

The list is parsed correctly in all of the versions before 12 and the LENGTH function returns 2, but in the latest version, it returns 1.

This is the console output in QtCreator  12:

This is the output of any older version:

Tested on macOS and Linux.