Paste attribute not enabled when an attribute is copied.

Copying an attribute ( **Edit** → **Node extensions** → **Copy attributes**) was enabling pasting that attribute ( **Edit** → **Node extensions** → **Paste attributes**). Opening another map (I used **Help**  → **Documentation**) *would* enable it because it sent the *checkOnPopup* signal *PasteAttributes* was listening for.  Changing the *EnabledAction* annotation from *checkOnPopup* to *checkOnPopup" fixed the issue.