Curtain Grids are one of those elements that folks have a love-hate relationship with. Working with Curtain Grids can be difficult at times, especially for the novice user. I've created a little video about what happens when you start to have smaller segments and the ability to actually see if a segment is visible or not.
When you use the Add/Remove Segment tool, grid segments that are visible should be solid and what is not currently visible should be dashed. The problem comes in when you have a short segment...it typically shows up solid even if it's not visible. What you can do is change the scale to be larger (1/4" instead of 1/8" for instance) for editing purposes, do what you need to do for adding and removing curtain grid segments, then change it back to the original scale. Or, just create a temporary elevation to edit your curtain grid segments.