In order for Autocad to know which block is which they have a name, but with dynamic blocks they can be altered so that they look different, in order for Autocad to keep track of these it gives them a second anonymous name, and the Autocad database uses these names internally, it also reports this name when you use the ATTEXT command (or when you use LIST), as a workaround I would add an attribute to the block and use that to keep the block name in.
Small addition: if the Dynamic Bloc is in its original position the BlockName will show.
If the position was changed (which is why we do dynamic blocks) it will show '*U'