I had this problem today morning. I saved everything before I close the app. But it asked me again if I want to save all the changes one more time after I clicked to close. And It said everything is ok and closed the app.
But when I tried to open my project it didnt work. It gave an error about the proj file and suggested me to look into it in a text editor and said it is in XML format. When I went to project folder I saw that the project file is 0 Kb. So it is empty. I saw an other file called xxx.capx.backup
I renamed the file and tried to load it and than I got an error which says error unzipping the file.
I tried to look into it with winrar and there was only one folder called animations. Nothing else.
I searched in the forum about this kind of problems and I saw a lot of complainings about it.
Some of them are written around 2011 then 2012 and 2013. So obviously this problem has not been considered as a huge problem over the last years but actually It is!
I have to start doing everything I have done from the beginning.
It is not cool.
Hope you will solve this problem in the new releases cause my code, my project has to be secured by the program that I created that project at the first place. Without no efforts and so on. But we have to be carefull about the program that we use to create the project and has to backup the files by ourselves! It is ironic.