I'm using Excel from Office 365 and am having an issue that I don't remember having in previous version. This is the issue: I open Excel from a desktop shortcut or the Start menu and a blank workbook/worksheet opens as normal. I then open a workbook/worksheet that I have saved from the pinned recent files. This opens another instance of Excel. If I then open another saved workbook in the same manner, again another instance of Excel opens. Previous versions, either replaced the the current workbook/worksheet with the new one or opened the next workbook/worksheet as a new tab. If I close the original workbook/worksheet, then all the open workbooks/worksheets close. I cannot find how to stop new instances opening.
Help please 

