Hello I would try to integrate the exemple Drag n Drop from http://spec.st/docs/drag_n_drop/ at the tutorial Building UI with Spec, so I have create a class in Pharo to try them and modify the code. I have found some of problems, I'm not sure if it come from strange configuration (i think about dragTransformationBlock: ), but it appear on the both version (my class and the original code). Marion, 1) Reproduce: Deplace the 'c' in the list of int, try to replace the 'c' in the list of char Error "nil not found in Orderred Collection" - Proceed don't remove the c from the list and make arrives a nil, like in the result deplaceReplaceC.png - Abandon seems work well, but the next refreshing of the list (by another move) make the nil appear too 2) Reproduce: Deplace the 3 in the list of char, try to replace the 3 in the list of int (at its place) Error " '3' not found in Orderred Collection" - Proceed duplicate the 3 gives the result DuplicateNumber.png - Abandon affect all number after the place, they "become" the previous number (BadNumber.png). Try to move the 4 make an error because it don't found 3, try to move the 5 make move the 4. 3) Reproduce: Deplace all items the list of int in the other Try to move the 'a' in the empty list of int Error "SubscriptOutOfBounds: 0" - Proceed remove the a from the list, but don't make it appear - Abandon seems work well