Duhh!! Yes I can repro in OS X 64-bit, thanks for the report Tycho!
a bit overloaded these days but i'll look into this as issue soon as I can (well already did, but looks like a tricky one: will create a ticket in the sws tracker & edit this post with the url, for the followup...).
Everything seems ok in 32-bit though, if you don't have other constraints may be you can use this in the meantime (?)
Also I know we're both talking about the same thing when it comes to "using REAPER live"
=> 2 things I want to add: this tool is used on stage but not on Mac yet, well as far as I know... also, do not hesitate to PM me if you plan to use this tool as such!