MS Powerpoint Addin : Insert Slide from Base 64 Powerpoint addin API does not carry over the original formatting of the slide

Question

https://learn.microsoft.com/en-us/javascript/api/powerpoint/powerpoint.presentation?view=powerpoint-js-preview#powerpoint-powerpoint-presentation-insertslidesfrombase64-member(1)

I'm currently using the above Powerpoint Addin API to insert slides from base 64. But the inserted slide doesn't seem to carry over all the original formatting from the original PPTX file(from which the base 64 string was created). Any ideas on why the original formatting wasn't applied during insert?

PowerPoint.run(function (context) {
                return context.sync.then(function(){
                    context.presentation.insertSlidesFromBase64(base64String),{
                        formatting: 'KeepSourceFormatting'
                    };
                    return context.sync()
                })
            });