What this tells me is that you and I don't pronounce our r-s in the same way. When I pronounce it, my tongue doesn't touch my palate at all, so there isn't any sh- position between t- and r-.

I know some people who barely pronounce their r-s even in words like road-race, and not at all in words like car-door; then again I know some others who distinctly pronounce them, and even throw them into words like wash that don't actually have them. I bet there's a huge body of literature on this variation in the formal linguistics research.

Ack; gotta go to work, but this has been most fascinating! :)