Frequent Tipster Leonid Nemirovsky says that in AutoCAD 2008/2009, Mtext formatting is a bit different than in previous releases. For example, you can highlight one line and center justify it, right justify the second line, and so on. This is a great feature, but if you open a drawing in an earlier version of AutoCAD, you can lose justifications that are perfect in 2008/2009. To prevent that from happening, try to do justifications or other MT settings the way you would do it in, say AutoCAD 2007. Simply saving a 2009 file as a 2007 does not make any difference. For example, if you create a three-line title under detail, make it top (or middle) center justified. Do not make it left justified and then change to center justified; that may cause a problem if the drawing is opened in AutoCAD 2007. Simple, but not the best way. Explode that title into single lines of text.
Notes from Cadalyst Tip Patrol: Text justification is very important for many reasons, and going back and forth through different versions of AutoCAD (or any software) can cause issues. If you know you are going to back save your files ahead of time, it helps to take steps like this. Because of the several small differences between releases, checking a file is a great idea, then you can use steps like this that Leonid sent to help fix the issues.