SVN Merge Between Sibling Branches

In SVN I have two branches, 1.0 and 2.0. If I fix an issue in 1.0, how do I merge that fix into 2.0 and vice versa?

Consider the following scenario:

1. I make a fix on the 1.0 branch and it creates a new file A (rev X).


2. I do a plain merge with just that fix from 1.0 to 2.0 (rev X+1)


3. I then make a fix on the 2.0 branch and it modifies A (rev Y).


4. If I merge that fix back to 1.0 I get a merge conflict!

I suppose I can always force that fixes are made on the 1.0 branch first or I could manually block the X+1 revision on the 1.0 branch. Both of these are non-ideal and I was wondering if there were a better way to handle sibling branches.

---