Entire touch window moved to background

When using the custom parameter page of an OP to set a file to load a video, the entire touchdesigner window is moved to the back of the windows stack.

OS: Windows 10 build 10.0.15063
TD: 099 Commercial 2017:37900

I have a base with a custom parameter page that I am using to let users select a video file from system.
It has a file and pulse parameter.

I have a button that when pressed opens the parameter page (op(‘…’).openViewer()) and the pulse open closes the window again when they have made a selection.

On first run through it works fine, but on subsequent loads (eg they want to change file) pressing either the window cross or pulsing closeviewer() moves the entire touch designer window to the rear of the windows OS window stack (basically it looks like touch is minimized )
close viewer test.toe (4.83 KB)