I have done a bit more testing and here is what I have found. If I highlight just the row with the checkbox in it I'm not able to get the multiple delete server behavior to rewrite the code for the button in this form. I tried a couple of other things and the only way I was able to get this to occur was if I highlighted both rows in that table in the form, or if I highlighted the entire table.
I think this must be what you are experiencing. I found that if I went into the split or code view and made the highlights it seemed to always select the portion of the table I was expecting. If I did the same thing in design view it seemed that it was easy to select the entire table or both rows in the table and it may not be known to you when you do this.
When I apply the repeat selection and go into code view the button is not within this area. If the button is within the repeat selection when I apply the multiple delete it rewrites the code on the button with the repeat selection increment variables. The next time you apply the repeat selection make sure to go into code view and check what is within the loop, if your button is in the loop you should move it out before applying the multiple delete to the page.