Hello Michel,
Normally you must install the base package (in your case 8.5.0.0), which contains the license (because you downloaded it from PA).
And then you might apply all the FixPack (which are found in the IBM Support page), which are normally without licenses.
Are you sure you can install 8.5.0.1 directly, without installing first 8.5.0.0?
Are you sure there are no files from 8.5.0.0 which were still on your system, and which gave the fixpack installation program a false-true info that 8.5.0.0 is already installed?
In all cases, if you install only the fixpack, half from the software is installed (only the parts that needs an update)... so I'm not sure you'll have the full CMOD installation with going only with step 2).
Cheers,
Alessandro