Nuvi 2x5 and later Nuvi 2x0 models add to the turn distance while driving

My Garmin nuvi 2x5 units and my nuvi 2x0 units that run the software that the 2x5s do (I think the SN's start with 1G....) will randomly add to the turn distance while driving. All that I've had done it are using Software Version 7.80 and have various different CN NA NT maps. For example, say I'm driving down the road, and it says I have 1.4 miles until my next turn. A little bit into that 1.4 miles, it just adds 1.4 miles to the turn distance, so it thinks I have 2.8 miles till my next turn. This means it won't say anything when I'm supposed to turn. I've contacted Garmin about this before and they said to try a master reset but that didn't fix anything. You guys have any ideas as to what's going on here and maybe how to fix it?