Wall junctions and endings

[KeesW]

I feel foolish asking this because I've been using AC for such a long time. But here goes: What determines a wall ending and it's junctions? I attach a small sketch of a wall corner. It isn't right because the horizontal wall end does not cleanly intersect the vertical wall, giving me an untidy corner in the plan view. I've copied the horizontal wall and put it under - it shows the dark green outside line returning at the end of the wall section - something I am unable to do with the real wall. I've also copied both horizontal and vertical walls and redrawn them underneath my plan - and they show a perfect corner.

There is something on the plan that is causing this but I don't know what.

I don't normally have this issue - walls are pretty fundamental - but this has me stumped.

[Barry Kelly]

Are all these walls in the same layer?
And are there any other walls in any hidden layers?
Barry.

[Anonymous]

Are the walls different heights, or are they overlapping with other walls from below or above?