[Dr. McKay]

So, if you're trying to modify an item while using the PRESERVE_ATTRIBUTES flag, you can't modify an existing attributes.

For example:

I have an Unusual hat. It is painted. I want to override the effect and change it. Doing so will remove the paint. If I use PRESERVE_ATTRIBUTES to try to keep the paint, no effect appears at all.

(Yes, I'm aware I can just reapply the paint attributes, but this is an example. This is actually happening automatically in a plugin).

Hope I'm clear enough...