diff --git a/writerfilter/qa/cppunittests/dmapper/DomainMapper.cxx b/writerfilter/qa/cppunittests/dmapper/DomainMapper.cxx
index 7cafcd19f280..ec771ba0f1b4 100644
--- a/writerfilter/qa/cppunittests/dmapper/DomainMapper.cxx
+++ b/writerfilter/qa/cppunittests/dmapper/DomainMapper.cxx
@@ -149,6 +149,12 @@ CPPUNIT_TEST_FIXTURE(Test, testSdtBlockText)
     xContentControlProps->getPropertyValue("Alias") >>= aAlias;
     CPPUNIT_ASSERT_EQUAL(OUString("myalias"), aAlias);
 }
+
+CPPUNIT_TEST_FIXTURE(Test, testFdo78333)
+{
+    // just care that it doesn't crash/assert
+    loadFromURL(u"fdo78333-1-minimized.docx");
+}
 }
 
 /* vim:set shiftwidth=4 softtabstop=4 expandtab: */
diff --git a/writerfilter/qa/cppunittests/dmapper/data/fdo78333-1-minimized.docx b/writerfilter/qa/cppunittests/dmapper/data/fdo78333-1-minimized.docx
new file mode 100644
index 000000000000..0c4a5bc67288
Binary files /dev/null and b/writerfilter/qa/cppunittests/dmapper/data/fdo78333-1-minimized.docx differ
diff --git a/writerfilter/source/dmapper/DomainMapper.cxx b/writerfilter/source/dmapper/DomainMapper.cxx
index e2ef4ec4a4b2..70fc7820844c 100644
--- a/writerfilter/source/dmapper/DomainMapper.cxx
+++ b/writerfilter/source/dmapper/DomainMapper.cxx
@@ -1192,9 +1192,6 @@ void DomainMapper::lcl_attribute(Id nName, Value & val)
                 m_pImpl->PushSdt();
                 break;
             }
-            if (m_pImpl->m_pSdtHelper->getControlType() == SdtControlType::plainText
-                && GetCurrentTextRange().is())
-                m_pImpl->m_pSdtHelper->setFieldStartRange(GetCurrentTextRange()->getEnd());
             m_pImpl->SetSdt(true);
         }
         break;
@@ -4229,7 +4226,6 @@ void DomainMapper::lcl_utext(const sal_Unicode *const data_, size_t len)
         {
             m_pImpl->m_pSdtHelper->createPlainTextControl();
             finishParagraph();
-            m_pImpl->m_pSdtHelper->setFieldStartRange(GetCurrentTextRange()->getEnd());
             return;
         }
     }
@@ -4487,10 +4483,9 @@ void DomainMapper::lcl_utext(const sal_Unicode *const data_, size_t len)
                 m_pImpl->clearDeferredBreaks();
             }
 
-            bool bSdtBlockUnusedText
-                = m_pImpl->m_pSdtHelper->GetSdtType() != NS_ooxml::LN_CT_SdtRun_sdtContent
-                  && m_pImpl->m_pSdtHelper->getControlType() == SdtControlType::plainText
-                  && m_pImpl->m_pSdtHelper->hasUnusedText();
+            bool bInSdtBlockText
+                = m_pImpl->m_pSdtHelper->GetSdtType() == NS_ooxml::LN_CT_SdtBlock_sdtContent
+                  && m_pImpl->m_pSdtHelper->getControlType() == SdtControlType::plainText;
             if (pContext && pContext->GetFootnote().is())
             {
                 pContext->GetFootnote()->setLabel( sText );
@@ -4500,32 +4495,29 @@ void DomainMapper::lcl_utext(const sal_Unicode *const data_, size_t len)
             }
             else if (m_pImpl->IsOpenFieldCommand() && !m_pImpl->IsForceGenericFields())
             {
-                if (bSdtBlockUnusedText)
+                if (bInSdtBlockText && m_pImpl->m_pSdtHelper->hasUnusedText())
                     m_pImpl->m_pSdtHelper->createPlainTextControl();
                 m_pImpl->AppendFieldCommand(sText);
-                if (bSdtBlockUnusedText)
-                    m_pImpl->m_pSdtHelper->setFieldStartRange(GetCurrentTextRange()->getEnd());
             }
             else if( m_pImpl->IsOpenField() && m_pImpl->IsFieldResultAsString())
             {
-                if (bSdtBlockUnusedText)
+                if (bInSdtBlockText && m_pImpl->m_pSdtHelper->hasUnusedText())
                     m_pImpl->m_pSdtHelper->createPlainTextControl();
                 /*depending on the success of the field insert operation this result will be
                   set at the field or directly inserted into the text*/
                 m_pImpl->AppendFieldResult(sText);
-                if (bSdtBlockUnusedText)
-                    m_pImpl->m_pSdtHelper->setFieldStartRange(GetCurrentTextRange()->getEnd());
             }
             else
             {
                 if (pContext == nullptr)
                     pContext = new PropertyMap();
 
+                if (bInSdtBlockText && !m_pImpl->m_pSdtHelper->hasUnusedText())
+                    m_pImpl->m_pSdtHelper->setFieldStartRange(GetCurrentTextRange()->getEnd());
+
                 m_pImpl->appendTextPortion( sText, pContext );
 
-                if (m_pImpl->m_pSdtHelper->GetSdtType() == NS_ooxml::LN_CT_SdtBlock_sdtContent
-                    && m_pImpl->m_pSdtHelper->getControlType() == SdtControlType::plainText
-                    && !sText.isEmpty())
+                if (bInSdtBlockText && !sText.isEmpty())
                     m_pImpl->m_pSdtHelper->setHasUnusedText(true);
             }
 
diff --git a/writerfilter/source/dmapper/SdtHelper.cxx b/writerfilter/source/dmapper/SdtHelper.cxx
index c7f99878e12d..922ac5bea106 100644
--- a/writerfilter/source/dmapper/SdtHelper.cxx
+++ b/writerfilter/source/dmapper/SdtHelper.cxx
@@ -604,6 +604,7 @@ void SdtHelper::clear()
     m_nId = 0;
     m_nTabIndex = 0;
     m_aLock.clear();
+    m_xFieldStartRange.clear();
 }
 
 void SdtHelper::SetPlaceholderDocPart(const OUString& rPlaceholderDocPart)