Wooden tail vice swells in changing seasons

I am nearing completion of a traditional work bench complete with a wooden tail vice. The vice was time consuming but came out pretty close to perfect and as I was staring at my accomplishment, I started to wonder if the runners that guide the vice would be subject to the same wood movement that rendered my table saw sled inoperable. I came home from vacation today and gave the vice a turn and noticed that it is very, very tight and squeaks very loud. What if anything can be done to prevent the vice from locking completely due to the swelling, and is this a normal problem for a wooden bench vice or have I made an error in some way. The bench is made of hard maple, but I used mahogany for the runners as that was all I had laying around my shop.

I will post this project just as soon as I can slap some finish on it. Thanks for your suggestions.

Here is a photo of the vice before he runners were added…
!http://www.flickr.com/photos/26283163@N03/2466004353/(Tail vice nearing completion)

-- Things of the greatest worth are from the Earth. Ben Harper