add the slot updateDisplayUnit() to overviewpage, sendcoinsdialog, sendcoinsentry and connect it to displayUnitChanged() - this ensures all fields in the GUI, who use a display unit are imediately updated, when the user changes this setting in the optionsdialog / ensure used fields init with the current set display unit

src/qt/overviewpage.cpp

@@ -152,7 +152,7 @@ void OverviewPage::setNumTransactions(int count)
 void OverviewPage::setModel(WalletModel *model)
 {
     this->model = model;
-    if(model)
+    if(model && model->getOptionsModel())
     {
         // Set up transaction list
         filter = new TransactionFilterProxy();
@@ -172,20 +172,26 @@ void OverviewPage::setModel(WalletModel *model)
         setNumTransactions(model->getNumTransactions());
         connect(model, SIGNAL(numTransactionsChanged(int)), this, SLOT(setNumTransactions(int)));
 
-        connect(model->getOptionsModel(), SIGNAL(displayUnitChanged(int)), this, SLOT(displayUnitChanged()));
+        connect(model->getOptionsModel(), SIGNAL(displayUnitChanged(int)), this, SLOT(updateDisplayUnit()));
     }
+
+    // update the display unit, to not use the default ("BTC")
+    updateDisplayUnit();
 }
 
-void OverviewPage::displayUnitChanged()
+void OverviewPage::updateDisplayUnit()
+{
+    if(model && model->getOptionsModel())
     {
-    if(!model || !model->getOptionsModel())
-        return;
         if(currentBalance != -1)
             setBalance(currentBalance, currentUnconfirmedBalance, currentImmatureBalance);
 
+        // Update txdelegate->unit with the current unit
         txdelegate->unit = model->getOptionsModel()->getDisplayUnit();
+
         ui->listTransactions->update();
     }
+}
 
 void OverviewPage::showOutOfSyncWarning(bool fShow)
 {

src/qt/overviewpage.h

@@ -44,7 +44,7 @@ private:
     TransactionFilterProxy *filter;
 
 private slots:
-    void displayUnitChanged();
+    void updateDisplayUnit();
     void handleTransactionClicked(const QModelIndex &index);
 };
 

src/qt/sendcoinsdialog.cpp

@@ -46,10 +46,11 @@ void SendCoinsDialog::setModel(WalletModel *model)
             entry->setModel(model);
         }
     }
-    if(model)
+    if(model && model->getOptionsModel())
     {
         setBalance(model->getBalance(), model->getUnconfirmedBalance(), model->getImmatureBalance());
         connect(model, SIGNAL(balanceChanged(qint64, qint64, qint64)), this, SLOT(setBalance(qint64, qint64, qint64)));
+        connect(model->getOptionsModel(), SIGNAL(displayUnitChanged(int)), this, SLOT(updateDisplayUnit()));
     }
 }
 
@@ -289,3 +290,12 @@ void SendCoinsDialog::setBalance(qint64 balance, qint64 unconfirmedBalance, qint
     int unit = model->getOptionsModel()->getDisplayUnit();
     ui->labelBalance->setText(BitcoinUnits::formatWithUnit(unit, balance));
 }
+
+void SendCoinsDialog::updateDisplayUnit()
+{
+    if(model && model->getOptionsModel())
+    {
+        // Update labelBalance with the current balance and the current unit
+        ui->labelBalance->setText(BitcoinUnits::formatWithUnit(model->getOptionsModel()->getDisplayUnit(), model->getBalance()));
+    }
+}

src/qt/sendcoinsdialog.h

@@ -47,8 +47,8 @@ private:
 
 private slots:
     void on_sendButton_clicked();
-
     void removeEntry(SendCoinsEntry* entry);
+    void updateDisplayUnit();
 };
 
 #endif // SENDCOINSDIALOG_H

src/qt/sendcoinsentry.cpp

@@ -68,6 +68,10 @@ void SendCoinsEntry::on_payTo_textChanged(const QString &address)
 void SendCoinsEntry::setModel(WalletModel *model)
 {
     this->model = model;
+
+    if(model && model->getOptionsModel())
+        connect(model->getOptionsModel(), SIGNAL(displayUnitChanged(int)), this, SLOT(updateDisplayUnit()));
+
     clear();
 }
 
@@ -82,10 +86,8 @@ void SendCoinsEntry::clear()
     ui->addAsLabel->clear();
     ui->payAmount->clear();
     ui->payTo->setFocus();
-    if(model && model->getOptionsModel())
-    {
-        ui->payAmount->setDisplayUnit(model->getOptionsModel()->getDisplayUnit());
-    }
+    // update the display unit, to not use the default ("BTC")
+    updateDisplayUnit();
 }
 
 void SendCoinsEntry::on_deleteButton_clicked()
@@ -160,3 +162,11 @@ void SendCoinsEntry::setFocus()
     ui->payTo->setFocus();
 }
 
+void SendCoinsEntry::updateDisplayUnit()
+{
+    if(model && model->getOptionsModel())
+    {
+        // Update payAmount with the current unit
+        ui->payAmount->setDisplayUnit(model->getOptionsModel()->getDisplayUnit());
+    }
+}

src/qt/sendcoinsentry.h

@@ -45,6 +45,7 @@ private slots:
     void on_payTo_textChanged(const QString &address);
     void on_addressBookButton_clicked();
     void on_pasteButton_clicked();
+    void updateDisplayUnit();
 
 private:
     Ui::SendCoinsEntry *ui;