There's a bunch of things in OS X Reaper that out of the box don't adhere to Mac convention (Command-H doesn't hide, opt-drag doesn't drag a copy, it moves the audio within the item; Command-drag drags a copy).
I just always chalked it up to its Windows origins and the Windows leanings of the devs. I feel grateful that they are as well versed in OS X as they are so I just accept that apps written for both, with the OS X version holding the position it does, are going to have a few of those that make me nuts. I mention the item copy-drag because every time I get back to Reaper after working on a project on anything else, I blow a few edits until I get back on board with the Windowsy way of doing it