SQL produced by Modify is missing a GO for SPs in SSMS
Whe you try and modify a procedure that has multiple versions the SQL produced is missing a GO between the alter procedure statements.
Primary Issue http://connect.microsoft.com/SQLServer/feedback/ViewFeedback.aspx?FeedbackID=125537 is marked as resolved in SP1 this issue isn't fixed in SP1
The primary item is not the same as this and is marked as not reproduceable. I can easily reproduce this on an SP1 box, using the repro steps