Line not showing due to mirror?

Hi there,

Please see the attachment for the part. In the top left corner, why does the corner merge to show only one visible piece? It should look like the top right corner, where the two structural members are split at at a 45 degree angle. For some reason, the mirror of the other parts is causing the two surfaces to merge.

Any ideas why this is happening?

Richard

SolidworksParts And Features