IVsBuildPropertyStorage.SetPropertyValue changes ';' into %3b

I'm trying to make a visual studio extension that fills a property with the following value "test.dll;anothertest.dll" when I use

buildPropertyStorage.SetPropertyValue(property, String.Empty, (uint)_PersistStorageType.PST_PROJECT_FILE, propValue);

to store the property it appears that the ";" has been replaced into "%3b". Which causes that MSBUILD is not recognizing it. 

How can I ensure that the ";" is written into the property?

Regards,

Rob