Running 2 separate sketches, can't select multiple ports

Hi. I'm trying to run 2 separate sketches but each time I try to change the port on either one, both sketches end up using the port I've just changed to. Just installed 1.6.5 on a macbook pro where the problem lies. Previously running on Linux which behaved as expected but an older version of the IDE.

So I'm not sure whether the problem is with the IDE or Apple. I'm unable to revert back to Linux to try 1.6.5.

Ok, sussed it. I had to open 2 instances of the IDE rather than just opening a second file from the first, which works fine from Linux but not OS X.