There is no really hot keys to open the UML modeller, but there is a TCP/IP server listing to a port for instructions to open the UML modeller.
I use that approach to get the Double click on an .uml file, to open the UML modeller.
Maybe something is triggering an "open this uml file" from the windows explorer.
Or (and more likely) someone sending some text on the port number the app is listing too.
Try these things:
Try renaming this folder:
C:\Program Files\National Instruments\LabVIEW 20XX\resource\Framework\Providers\Open_GDS\UmlMessage
To make sure Windows can't find the application linked to the uml extension.
These exe files just sends a TCP/IP request to this VI:
C:\Program Files\National Instruments\LabVIEW 20XX\resource\Framework\Providers\Open_GDS\SubVIs\GOOP_TcpIpListener.vi
Or Activate the debug feature by creating a file called: DebugLog.txt and place it in this folder: C:\data\LabVIEW Data\Open_GDS
Then start LabVIEW and examine the debug file next time LV open's the uml modeller.
And also send me a copy of it.