When placing glass panes, the white stripes that usually appear around the edge of connected glass panes will randomly appear in the middle, instead.

What I expected to happen was...:
When placing several glass planes together (connected) they should create one solid sheet, with no lines through the middle. (The 2-3 dots that appear are expected, and normal.)

What actually happened was...:
When placing several glass panes together (connected) they sometimes create 1 solid sheet of glass with no lines (except the random placement of dots), but other times will have vertical lines running down them.

Steps to Reproduce:
1. Create 2 (or more) openings that are the same size and shape.
2. Place glass panes in each opening.
3. Some will appear as solid sheets, some will have vertical lines in them.