Normally, when you draw a polyline with a non-continuous linetype (like HIDDEN or CENTER), the linetype stops and starts at each vertex. This ensures that there is a solid line at each corner. However, sometimes this isn't the desired effect, usually because the distance between vertices is too short to display the linetype. If this happens, simply click on the polyline, open the Properties dialog box, and go to the bottom for the "Linetype Generation" option (under "Misc"). Change it to "Enabled" -- now the linetype stops at the beginning of the polyline and goes all the way to the end, so even short segments can display the correct pattern.