I have a strange case here. The case happen to both Firebird 3.0 and 4.0.

Here are the steps:

1. In Windows, install x64 firebird from setup file.
2. Make sure the firebird service is running and listen to port 3050.
3. I use firebird OO API like fb_get_master_interface: IMaster to test
4. Connect to localhost:employee and close the connection.
5. Without closing the application, using IMaster.getDispatcher.createDatabase to create an embedded database using hostless URI and an error shall prompt:

	MappingIpc: Cannot initialize the shared memory region
	Shared memory area is probably already created by another engine instance in another Windows session

By reversing the steps:

1. In application, using IMaster.getDispatcher.createDatabase to create an embedded database using hostless URI
2. Without closing application, connect to localhost:employee andit prompt same error:

	MappingIpc: Cannot initialize the shared memory region
	Shared memory area is probably already created by another engine instance in another Windows session

Using same fbclient.dll and access localhost:employee (open and close) followed by create an hostless database raise the exception.