Whenever any block that is not a full block (including ones from other mods) is placed above a road or sidewalk block, the road/sidewalk block turns invisible. Also if a streetlight from any mod including this one is placed, the block(s) below will turn invisible.
This was a problem in the 1.1 final build. You can either use the 1.2 beta builds (which have some incomplete creative-only features that can be ignored or experimented with) or an earlier 1.1 build
Whenever any block that is not a full block (including ones from other mods) is placed above a road or sidewalk block, the road/sidewalk block turns invisible. Also if a streetlight from any mod including this one is placed, the block(s) below will turn invisible.