I was able to reproduce this in the github release branch.
To reproduce:
- Add a SM and a BPActor to a Level.
- Select the SMActor and then use SHIFT+RMB when clicking on the Transform category in the property editor. (this copies the properties under that category to your clipboard)
- Select the BPActor and then use SHIFT+LMB when clicking on the Transform category in the property editor. (this pasts the clipboard on top of the properties under that category)
The reason this does not work is because SMActors have a customization that adds the Mobility SceneComponent property to the Transform category. Hence, in 5.4.2, this property is now present in the clipboard text. This property is not present under the Transform category of the BPActor and, when pasting, the paste will be rejected due to a mismatch in numbers of properties in SDetailCategoryTableRow::CanPasteCategory.
I suspect that SDetailCategoryTableRow is being too restrictive here.