Hello,
I have done some tests on our end and I was indeed able to reproduce the described behavior.
Unfortunately, I can not really say why this is happening nor was I able to find a workaround for this beside the one presented by you (to add the prerequisite as a feature-based prerequisite).
I have forwarded this to our development team for further investigation and hopefully a fix will be available in a future version of Advanced Installer.
Thank you for bringing this to our attention!
Note that as Feature Based works fine with /PW=aa[\!]bbb[\!]ccc
Please note that, when the prerequisite is added as a feature-based prerequisite, you can simply pass the property normally, e.g.:
In Advanced Installer UI for the project I see the [\!] in red color only when is a Feature Based.
The character is displayed in the red color because, by default, Windows Installer properties are enclosed between the "[]" characters.
It is shown in red for the "feature-based" prerequisite because, during the time pre-install prerequisites are installed, Windows Installer properties (the one from the main package) are not available.
Best regards,
Catalin