Thanks Febrillian,
Good to hear that I'm not the only one,
I've faced similar issues with editing cells. If I click on cell C3 and I visit another cell the Dashboards program copies the contents of cell C3 in the other cell !. This is very frustrating and time consuming.
Downgrading Excel is not an option for me since I've got a full functioning Office 2013 suite with Outlook, Onenote etc.
According to the PAM (as Amr pointed out) this IS a supported platform so it should be fixed. As I wrote before it could also be a MS bug.
Thank you all for your comments.
I will try to report this is a product defect.