I tested this bug with all types of fences, with all types of fence gates, with classic glass panel and with iron bars. The sand get stucked at all of possibilities excluding the glass panel and the iron bars. (see the pictures). Next I tried another possiblities, e.g. with falling gravel (result was same) and with another block, but in most cases the sand got broken into item (e.g. falling sand onto a stone slab)