Using Evernote Premium 18.104.22.16844 (303244) on Windows 7 pro x64 and dealing with an Excel xlsx attachment:
I am dealing with similar things here. The issues and reasoning behind the behavior is well described above. Thanks for everyone's input, it helped!
Evernote seems to update the file saved within the note immediately when I do a save but, I have noticed that sometimes my system fails to close out the "EXCEL.EXE *32" process when I close the Excel application. The files get left behind in the attachments folder when this occurs. If I open the task manager (Ctrl-Shift-Esc) and kill the process this triggers Evernote to release the file (Filename.xlsx) and the file is automatically deleted out of the attachments folder (Evernote does keep a backup of many of the files there as a .backup file, these can be deleted if all is well). My system is unpredictable as to when it will close the Excel application but not kill the EXCEL.EXE *32 process. There must be something residual that Excel is still trying to deal with? After I kill the process manually Things function properly again and I temporarily don't get the file duplication with the , , , numbering. Yay! The residual temp files in the attachment folder don't seem to affect the the file saved to the Evernote note, they just make a mess.