Drag and Drop Not Working

I have an EggPlant Functional script that needs to move a window on a Windows desktop.
When I run the script, the cursor moves to the desired location, but the window doesn't move. However, when stepping through the script with the debugger, the window moves correctly.

I have tried using both the DragandDrop and separate Drag and Drop commands with the same result. I have tried playing with the Mouse Move Speed and Mouse Drag Speed in the Run settings, but it doesn't help.

Any ideas about what could be causing this, or suggested fixes?
I am using UltraVNC to connect to my SUT. Could that have something to do with it?

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