when you are drawing your lines have you checked the properties of the line? do they have a fill or stroke on them? can you show a full screenshot before you join the layers and with one of the line layers selected?
The only way I can replicate what you have is when I have the lines underneath the box layer and that is filled..?
Thanks for your help. The below is what I have just before merging the three shapes in the Layers panel into one only to see the crossed lines turn empty except for their outlines.
As you can see, the Fill is disabled and the Stroke is set to black. At the same time the line objects are above the rectangle.
I think the two lines should remain filled with black without being empty. Is this just a bug?
Have you tried just filling the lines instead of using stroke on them?
Ok lets see if I can walk you through this....
New document > 200x150px 72ppi (pick a colour background for this test)
View > Snap
View > Show > Pixel Grid
Shape tool (U) > Rectangle
Click on artboard set 80x50px, OK
Layer still selected set stroke to 1px Black no fill
Zoom in so full screen
Shape tool > Line tool set weight 1px
click and drag from the INSIDE corner bottom left to top right
layer still selected with (U) fill black
Duplicate this layer (Ctrl+J)
Transform (Ctrl+T) Flip Horizontal
Select layers and Convert to smart object...
Here is my screen...
Thank you for the schematics. Convert to Smart Object always works fine. It's only Merge Shapes which get rid of the crossed lines.
All the same, I've managed to create a proper wireframe for a major website and will keep using Convert to Smart Object for the same purpose.