Hi, first post here so yeah this is whats up:

In the image below you can see some lines parallel to my red ones, now I had a square drawn between them, from the back of the extruding lower parts to the front where my lines end. just an empty square but for some reason those couple of lines got drawn inside my square and I couldn't select it as a whole, it was cut along these lines.
I can't select them, I can't erase them even when I redraw the square.
The only way they disappear is when I delete some of the nearby geometry of the parts you can still see but even when I then redraw it they come back.

Can't figure this out
Posting this here because I'm not sure if it's a noob thing or a bug.
I'm not really new to sketchup but I'm certainly no pro, just use it occasionally, never seen this though.

Woodworking/millimeter template on a windows 7, if that might be relevant.