diff --git a/src/ca/cac.cpp b/src/ca/cac.cpp
index 0317f2145..8a756c746 100644
--- a/src/ca/cac.cpp
+++ b/src/ca/cac.cpp
@@ -333,6 +333,12 @@ cac::~cac ()
 
     this->ipToAEngine.release ();
 
+    // clean-up the list of un-notified msg objects
+    while ( msgForMultiplyDefinedPV * msg = this->msgMultiPVList.get() ) {
+        msg->~msgForMultiplyDefinedPV ();
+        this->mdpvFreeList.release ( msg );
+    }
+
     errlogFlush ();
 
     osiSockRelease ();
@@ -606,6 +612,8 @@ void cac::transferChanToVirtCircuit (
             msgForMultiplyDefinedPV * pMsg = new ( this->mdpvFreeList )
                 msgForMultiplyDefinedPV ( this->ipToAEngine, 
                     *this, pChan->pName ( guard ), acc );
+            // cac keeps a list of these objects for proper clean-up in ~cac
+            this->msgMultiPVList.add ( *pMsg );
             // It is possible for the ioInitiate call below to
             // call the callback directly if queue quota is exceeded.
             // This callback takes the callback lock and therefore we
@@ -1297,6 +1305,8 @@ void cac::pvMultiplyDefinedNotify ( msgForMultiplyDefinedPV & mfmdpv,
         epicsGuard < epicsMutex > guard ( this->mutex );
         this->exception ( mgr.cbGuard, guard, ECA_DBLCHNL, buf, __FILE__, __LINE__ );
     }
+    // remove from the list and delete msg object
+    this->msgMultiPVList.remove ( mfmdpv );
     mfmdpv.~msgForMultiplyDefinedPV ();
     this->mdpvFreeList.release ( & mfmdpv );
 }
diff --git a/src/ca/cac.h b/src/ca/cac.h
index 63acccb6f..96cb19a78 100644
--- a/src/ca/cac.h
+++ b/src/ca/cac.h
@@ -237,6 +237,7 @@ private:
     resTable < tcpiiu, caServerID > serverTable;
     tsDLList < tcpiiu > circuitList;
     tsDLList < SearchDest > searchDestList;
+    tsDLList < msgForMultiplyDefinedPV > msgMultiPVList;
     tsFreeList 
         < class tcpiiu, 32, epicsMutexNOOP > 
             freeListVirtualCircuit;
diff --git a/src/ca/msgForMultiplyDefinedPV.cpp b/src/ca/msgForMultiplyDefinedPV.cpp
index 2f1a45cde..7002dd4b9 100644
--- a/src/ca/msgForMultiplyDefinedPV.cpp
+++ b/src/ca/msgForMultiplyDefinedPV.cpp
@@ -55,8 +55,10 @@ msgForMultiplyDefinedPV::~msgForMultiplyDefinedPV ()
 
 void msgForMultiplyDefinedPV::transactionComplete ( const char * pHostNameRej )
 {
+    // calls into cac for the notification
+    // the msg object (= this) is being deleted as part of the notification
     this->cb.pvMultiplyDefinedNotify ( *this, this->channel, this->acc, pHostNameRej );
-    // !! dont touch this pointer after this point because object has been deleted !!
+    // !! dont touch 'this' pointer after this point because object has been deleted !!
 }
 
 void * msgForMultiplyDefinedPV::operator new ( size_t size, 
diff --git a/src/ca/msgForMultiplyDefinedPV.h b/src/ca/msgForMultiplyDefinedPV.h
index 45d3453ac..3f1e771c0 100644
--- a/src/ca/msgForMultiplyDefinedPV.h
+++ b/src/ca/msgForMultiplyDefinedPV.h
@@ -33,6 +33,7 @@
 
 #include "ipAddrToAsciiAsynchronous.h"
 #include "tsFreeList.h"
+#include "tsDLList.h"
 #include "compilerDependencies.h"
 
 #ifdef msgForMultiplyDefinedPVh_epicsExportSharedSymbols
@@ -47,7 +48,9 @@ public:
         const char * pAcc, const char * pRej ) = 0;
 };
 
-class msgForMultiplyDefinedPV : public ipAddrToAsciiCallBack {
+class msgForMultiplyDefinedPV :
+        public ipAddrToAsciiCallBack,
+        public tsDLNode < msgForMultiplyDefinedPV >  {
 public:
     msgForMultiplyDefinedPV ( ipAddrToAsciiEngine & engine,
         callbackForMultiplyDefinedPV &, const char * pChannelName, 
@@ -62,8 +65,8 @@ private:
     ipAddrToAsciiTransaction & dnsTransaction;
     callbackForMultiplyDefinedPV & cb;
     void transactionComplete ( const char * pHostName );
-	msgForMultiplyDefinedPV ( const msgForMultiplyDefinedPV & );
-	msgForMultiplyDefinedPV & operator = ( const msgForMultiplyDefinedPV & );
+    msgForMultiplyDefinedPV ( const msgForMultiplyDefinedPV & );
+    msgForMultiplyDefinedPV & operator = ( const msgForMultiplyDefinedPV & );
     void operator delete ( void * );
 };
 
diff --git a/src/libCom/misc/ipAddrToAsciiAsynchronous.cpp b/src/libCom/misc/ipAddrToAsciiAsynchronous.cpp
index 09742e8a3..6dbdc405e 100644
--- a/src/libCom/misc/ipAddrToAsciiAsynchronous.cpp
+++ b/src/libCom/misc/ipAddrToAsciiAsynchronous.cpp
@@ -264,12 +264,16 @@ void ipAddrToAsciiEnginePrivate::run ()
                 continue;
             }
 
+            // fix for lp:1580623
+            // a destructing cac sets pCurrent to NULL, so
+            // make local copy to avoid race when releasing the guard
+            ipAddrToAsciiTransactionPrivate *pCur = this->pCurrent;
             this->callbackInProgress = true;
 
             {
                 epicsGuardRelease < epicsMutex > unguard ( guard );
                 // dont call callback with lock applied
-                this->pCurrent->pCB->transactionComplete ( this->nameTmp );
+                pCur->pCB->transactionComplete ( this->nameTmp );
             }
 
             this->callbackInProgress = false;