Sometimes there is a delay to respect when selecting a buiding to build in the UI . If I shift-click on the building to build and go right to map to place it , a selection box appears instead of the shape of the building it doesn' t happens always but quite regurlary,also I don't think it happens with a plain click nevertheless there is stil a delay for the click to be registered . See on the first video. Rarely the box remains fixed and mix up the selection process until the map is clicked again see on the second video.Once selection became impossible with unit vanishing and reappearing with no recovery I could find no video for this one.
build selection delay video
Fixed box video