Army Grouping - custom formation problem

[Glasgif]

When I group my men together just the way I want it and do crtl + 1 (or hit the group button on the interface), and then then right click on a new location, my current formation sometimes breaks into a single line rather than my own formation. What is causing this? Half of the time my men follow the exact formation I made and the other half do a single line, why?

[Nemotrox]

This happened to me, if any unit is currently moving in that formation when you click then the new formation will be a single line. Just make sure all your units are stopped or do a quick halt and they should then keep formation

[dunehunter]

Another solution to this is to ungroup them for one moment when you give the movement order, then group them again. This also allows you to change how deep they deploy and things like that.