This may/may not be valid.

This morning I was on 10m looking for 7O73T and saw a bunch of <. . . .> since I had not seen 7O73T as of yet.  After a couple of passes with no 7O73T in sight, I just added his call to the DX Call box as I normally do, and on the next pass, the <. . .> were now replaced with 7O73T even though I had not seen him yet.  

In testing later, putting the S20MUJ did NOT do the same thing.  

There is a hashtable erase in WSJTx for WSPR, but not everything else.