The path is cleared by the installer of the SDK.
The behavior (clear or append) actually depends on the length of the variable PATH.
After some tests, it seems that if the length is less than 1023 characters, then the installer attempts to append the path of the Bin directory. If the length is longer than 1023 characters, the installers issues following message:
PATH was empty and has been updated by target
Then the PATH is overwritten.
Also, the behavior is not the expected one if the length of the PATH is between 960 characters and 1023. In this case, the installer attempts to append the Bin directory to the PATH, but writes only the first characters until the global length reaches 1023.
If you want to try this out, set your PATH variable to following content:
C:\Program Files (x86)\myLibrary1\bin;C:\Program Files (x86)\myLibrary2\bin;C:\Program Files (x86)\myLibrary3\bin;C:\Program Files (x86)\myLibrary4\bin;C:\Program Files (x86)\myLibrary5\bin;C:\Program Files (x86)\myLibrary6\bin;C:\Program Files (x86)\myLibrary7\bin;C:\Program Files (x86)\myLibrary8\bin;C:\Program Files (x86)\myLibrary9\bin;C:\Program Files (x86)\myLibrary10\bin;C:\Program Files (x86)\myLibrary11\bin;C:\Program Files (x86)\myLibrary12\bin;C:\Program Files (x86)\myLibrary13\bin;C:\Program Files (x86)\myLibrary14\bin;C:\Program Files (x86)\myLibrary15\bin;C:\Program Files (x86)\myLibrary16\bin;C:\Program Files (x86)\myLibrary17\bin;C:\Program Files (x86)\myLibrary18\bin;C:\Program Files (x86)\myLibrary19\bin;C:\Program Files (x86)\myLibrary20\bin;C:\Program Files (x86)\myLibrary21\bin;C:\Program Files (x86)\myLibrary22\bin;C:\Program Files (x86)\myLibrary23\bin;C:\Program Files (x86)\myLibrary24\bin;C:\Program Files (x86)\myLibrary25\bin;C:\Program Files (x86)\myLibrary26\bin;C:\Program Files (x86)\myLibrary27\bin
These 1043 characters are simply overwritten by the installer.
Regards
Steph