Exports of xls files open in a small window in the lower right corner

I'm now at the second organization where multiple users including myself are experiencing some sort of visual bug where xls exports from Marketo open in a very small window in the lower right corner of our Macs. Csv files seem to open fine, and other xls/xlsx files from other sources open normally, it's only Marketo xls (campaign results, reports, etc) files that do this - does this occur for anyone else, and has anyone found a setting or permission in Marketo or Excel for Mac that prevents this?