Yes, the connector label "tilted" has a "Top Margin" set at 40 pt, whereas all other margins are set to 2 pt. To fix, highlight the line/text then from the HOME ribbon (1) click on the small arrow in the lower right-hand corner of the FONT selection (The text dialog menu will appear). Then (2) click on the "Text Block" at the top of that menu. Under "Margins" reset the value from "40 pt" to "2 pt". That should cure your problem.

On another note, if the text does continue to change its orientation, you can add the "Rotate Text" icon to your "Quick Access Toolbar" at the top of the Visio page. Once you do that, just click on the text the click on the Rotate Text icon until you text is in the correct postion. (In this particular case, it would be easier to delete the existing line and replace the connecter and text altogether).

Hope this helps...