I noted 2 bugs with Groupy 1.02 when using with Excel 2013
1. Sometimes when I have several Excel files grouped in tabs, when I'm typing into a cell, suddenly what I'm typing is not being entered into the foreground file but I realise moments later it was typed into a background file. This shift of focus happens randomly without any apparent pattern. It's dangerous because I could be overwriting content in another file since it's not visible to the user. Not sure if you can understand what I'm describing...?
2. When opening an Excel file attachment from an email, it will normally launch in Protected View. Now assuming I have several Excel files grouped together including one in Protected View. Now, when I click on "Enable Editing" to disable protected view, the result is an empty window for that particular file. I have a taken a video of this issue which I can send to Stardock if I can have the email address.