Overlap is incorrect calculated

[eL-Prova]

There is a bug while adding widgets. I build the gridster and then get the widgets from the database which are added to the grid. The steps to reproduce:

• gridster has 3 columns
• Add widget at x = 1, y =1 by add_widget method (with col and row)
• Add second widget with again x = 1, y = 1 (col and row not given) (goes correct, is added after the first one)
• move first widget on position of second. (result is second is position 1, first on position 2)
• add widget x = 1, y = 1 (without col and row) (BREAK)

Result is that on position 1 the second and last image are set.