I am having this problem on both MyEclipse 5.0.1 and 5.1 on Windows Server 2003
I create a collaboration diagram, in it I put 3 Classifier roles and link them together by association lines. On these lines I add 2 messages “1: test1” and “2: test2” and the diagram is now the way I want it. After I close the UMR tab and reopen it, the number has all been reverted back to 1.
This is reproducable when creating a new umr file is created or when adding a diagram to an existing one.