Sandy, not so far. The edge of the scanner platen seems to be fairly well sealed, but I take care to try and avoid using so much fluid that it runs to the edges. If I overdo it, I soak up the extra with my microfiber cloth. I am using KAMI, so it evaporates quickly, too.

My piece of plex is roughly 5x7 and sits in the middle of the bed with the mylar overhanging on the near edge to make it easy to grasp and lift. With the plex so far from the edges, it makes intercepting any excess fluid fairly easy.