Make sure to clean up mapBlockSource if we've already seen the block

Credit TheBlueMatt

src/net_processing.cpp

@@ -2134,9 +2134,12 @@ bool static ProcessMessage(CNode* pfrom, const std::string& strCommand, CDataStr
             }
             bool fNewBlock = false;
             ProcessNewBlock(chainparams, pblock, true, &fNewBlock);
-            if (fNewBlock)
+            if (fNewBlock) {
                 pfrom->nLastBlockTime = GetTime();
-
+            } else {
+                LOCK(cs_main);
+                mapBlockSource.erase(pblock->GetHash());
+            }
             LOCK(cs_main); // hold cs_main for CBlockIndex::IsValid()
             if (pindex->IsValid(BLOCK_VALID_TRANSACTIONS)) {
                 // Clear download state for this block, which is in
@@ -2211,8 +2214,12 @@ bool static ProcessMessage(CNode* pfrom, const std::string& strCommand, CDataStr
             // Since we requested this block (it was in mapBlocksInFlight), force it to be processed,
             // even if it would not be a candidate for new tip (missing previous block, chain not long enough, etc)
             ProcessNewBlock(chainparams, pblock, true, &fNewBlock);
-            if (fNewBlock)
+            if (fNewBlock) {
                 pfrom->nLastBlockTime = GetTime();
+            } else {
+                LOCK(cs_main);
+                mapBlockSource.erase(pblock->GetHash());
+            }
         }
     }
 
@@ -2390,8 +2397,12 @@ bool static ProcessMessage(CNode* pfrom, const std::string& strCommand, CDataStr
         }
         bool fNewBlock = false;
         ProcessNewBlock(chainparams, pblock, forceProcessing, &fNewBlock);
-        if (fNewBlock)
+        if (fNewBlock) {
             pfrom->nLastBlockTime = GetTime();
+        } else {
+            LOCK(cs_main);
+            mapBlockSource.erase(pblock->GetHash());
+        }
     }