diff --git a/nw/gui/elements/doceditor.py b/nw/gui/elements/doceditor.py
index a0baeb74..3e0aba3c 100644
--- a/nw/gui/elements/doceditor.py
+++ b/nw/gui/elements/doceditor.py
@@ -258,7 +258,7 @@ class GuiDocEditor(QTextEdit):
 
     def updateDocMargins(self):
         """Automatically adjust the margins so the text is centred, but
-        only if Config.textFixedW is set to True.
+        only if Config.textFixedW is enabled or we're in Zen mode.
         """
 
         if self.mainConf.textFixedW or self.theParent.isZenMode:
@@ -281,7 +281,13 @@ class GuiDocEditor(QTextEdit):
         docFormat = self.qDocument.rootFrame().frameFormat()
         docFormat.setLeftMargin(tM)
         docFormat.setRightMargin(tM)
+
+        # Updating root frame triggers a QTextDocument->contentsChange
+        # signal, which we do not want as it re-runs the syntax
+        # highlighter and spell checker, so we block it briefly.
+        self.qDocument.blockSignals(True)
         self.qDocument.rootFrame().setFrameFormat(docFormat)
+        self.qDocument.blockSignals(False)
 
         return
 
diff --git a/nw/guimain.py b/nw/guimain.py
index 8f658ce0..95e0c6a3 100644
--- a/nw/guimain.py
+++ b/nw/guimain.py
@@ -106,11 +106,13 @@ class GuiMain(QMainWindow):
         self.viewPane.setLayout(self.docView)
 
         self.splitView = QSplitter(Qt.Horizontal)
+        self.splitView.setOpaqueResize(False)
         self.splitView.addWidget(self.editPane)
         self.splitView.addWidget(self.viewPane)
 
         self.splitMain = QSplitter(Qt.Horizontal)
         self.splitMain.setContentsMargins(4,4,4,4)
+        self.splitMain.setOpaqueResize(False)
         self.splitMain.addWidget(self.treePane)
         self.splitMain.addWidget(self.splitView)
         self.splitMain.setSizes(self.mainConf.mainPanePos)