STR 1. Open devtools CSS inspector. 2. Disable a property. 3. Copy the rule to a document. Result The disabled property still appears in the rule. Consequently, the target of copy&paste has different CSS from the source. Expected result The property should be commented out when copied.

Very good idea! Thanks for the bug report. Somehow related: when disabling properties, they should then appear commented out too in the style-editor, but that's a bigger topic related to rule-view/style-editor synchronization.

(I should add that the idea is not mine, but that of a semi-anonymous user through the Contribute page.)