וְלֹא תִסֹּב נַחֲלָה מִמַּטֶּה לְמַטֶּה אַחֵר
A slightly embarassing story: A number of years ago, I was all ready for this פסוק and when the בעל קריאה pronounced it לְמַטֵּה אַחֵר I pounced on him and corrected him. One of the גבאים then corrected me and showed me that his חומש clearly said לְמַטֵּה.
First, let me clarify my position. When I was going over the פרשה the night before, I noticed that the תרגום of למטה אחר was "לשבטא אחרנא". This would mean that the term is translated as "another tribe." Pronouncing it לְמַטֵּה would give it סמיכות and it would then be understood as "the tribe of another. If that were the proper form, the תרגום would have been "לשבטא דאחרנא." The former also seemed to be the more intuitive understanding of the words. I was therefore quite confident that this was the right pronunciation and לְמַטֵּה would distort the meaning of the word.
It turns out I wasn't completely wrong. As the ספר אם למקרא points out, there is a מחלוקת as to how this word is to be pronounced. Indeed, R' Breuer, on whom my חומש was based, says it should be לְמַטֶּה . But there are others who disagree. The בעל קריאה actually called me in the middle of the week to acknowledge this and stated that had he known, he would have made sure to pronounce it לְמַטֶּה in accordance with R' Breuer.
Nevertheless, when פ' מסעי comes around every year, I make sure to keep my mouth shut on this פסוק.