Importing *some* Mermaid diagrams imports as image even with diagram selected

[bricin]

1. Open a new diagram
2. Arrange -> Insert -> Mermaid
3. In the Mermaid box, insert the text from your diagram
4. Select Diagram

Result: for some simple Mermaid diagrams, this is now an editable diagram. But for other Mermaid (see below) this results in an image being created.

v29.2.3 in Google Chrome on MacOS. Also repros in v29.0 Electron build on Mac.

Mermaid that doesn't import as diagram

C4Context
title Level 1 System Context - Air Freight Logistics

Person(shipper, "Shipper", "Sends goods requiring air freight")
Person(recipient, "Recipient", "Receives delivered goods at destination airport")
Person(airport_ops, "Airport Operator", "Manages landing and unloading slots")

Enterprise_Boundary(b0, "Air Freight Logistics System") {
    System(afl_system, "Air Freight Logistics Platform", "Manages carrier operations, flight scheduling, airport slot allocation, and delivery coordination from order to final airport delivery")
    SystemDb(afl_db, "AFL Database", "Stores Bills of Lading/Air Waybills, flight schedules, slot availability, traffic data")
}

System_Ext(carriers, "Carrier Nodes", "DHL, CargoLux, Fedex - Accept orders and manage flights with goods")
System_Ext(airports, "Airport Nodes", "SEA, LAX, DEN, JFK, ATL, ONT - Manage landing/unloading slots and capacity")
System_Ext(atm, "Air Traffic Management", "FAA/EASA-like system - Manages congestion, slot availability, and traffic routing")
System_Ext(forwarders, "Freight Forwarders", "Coordinate logistics, customs, and regulatory compliance")
System_Ext(regulators, "Regulatory Bodies", "Enforce compliance and safety requirements")

Rel(shipper, carriers, "Places shipment order")
Rel(carriers, afl_system, "Submits Waybill/AWB, requests flight slots")
Rel(afl_system, airports, "Requests landing/unloading slots")
Rel(afl_system, atm, "Queries traffic congestion and slot availability")
Rel(afl_system, forwarders, "Coordinates freight forwarding")
Rel(afl_system, regulators, "Reports compliance data")
Rel(afl_system, afl_db, "Reads/writes order and flight data")
Rel(afl_system, recipient, "Delivers goods to destination airport")
Rel(airports, atm, "Reports capacity and slot status")