This seems to be a new bug with Release 221 - have a copper shovel in left had, stale red/light red sand in right how. both in top right of wheel and set to active. then use the shovel on sand. you will notice that the right hand will activate every few swings or pieces like it is attempting to place the block down.
I wasn’t able to recreate this with other blocks.
I did even restart computer and tried on 2 characters on Biitula in my beacon. Same results.