Subtract function leaves fine line

[ElEstragos]

I couldn’t find if this was answered anywhere so I apologize if it is. 

I am having an issue that when I use the subtract operation the object is being subtracted but it leaves a fine line. When switched to nodes and zoomed in it appears that the outer most edge of the shape still exists but the centre is cut out. I though that after a first attempt my top shape to be cut out just wast big enough and was inside the bottom shape but when tried again and making sure my top shape extended beyond the borders of the bottom shape the line is still there. What am I doing wrong? 

Thanks for the help

[MEB]

Hi ElEstragos,
Welcome to Affinity Forums
You are probably seeing the background colour bleeding through the antialiased edges of the two objects. If their edges match exactly (no boolean operation errors) then that's mostly the cause, but without seeing the file i can't guarantee it. This is a known side effect of how the rendering engine works. See this thread for more info/details. Some ways to work around this is placing a background shapes with a similar colour of the foreground objects, adding a stroke to the objects (to cover the antialiased area) or adjusting the coverage map of these objects to change the way they are antialiased (see image below for reference - the coverage map was applied to the center object on the bottom group).