Browser window jumping when click on custom navigation button

When testing a course through our LMS (Cornerstone)  in Internet Explorer, any time a user clicks on a custom button causes the browser window containing the course to jump behind any other open browser window (which is generally the LMS itself). 

The course plays fine in Chrome as well as on Scorm Cloud. Using Articulate 360.

Anyone else ever experience this issue and know what causes it, how to resolve it? 

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