diff --git a/include/DetachableWidget.h b/include/DetachableWidget.h
index 12228e49728..532dec3303f 100644
--- a/include/DetachableWidget.h
+++ b/include/DetachableWidget.h
@@ -36,7 +36,7 @@ class LMMS_EXPORT DetachableWidget : public QWidget
 {
 	Q_OBJECT
 public:
-	explicit DetachableWidget(QWidget* parent = nullptr, Qt::WindowFlags f = Qt::WindowFlags{});
+	using QWidget::QWidget;
 
 	void closeEvent(QCloseEvent* ce) override;
 
diff --git a/include/DetachableWindow.h b/include/DetachableWindow.h
index bf3aa7b1aca..1636b4fad25 100644
--- a/include/DetachableWindow.h
+++ b/include/DetachableWindow.h
@@ -36,7 +36,7 @@ class LMMS_EXPORT DetachableWindow : public QMainWindow
 {
 	Q_OBJECT
 public:
-	explicit DetachableWindow(QWidget* parent = nullptr, Qt::WindowFlags f = Qt::WindowFlags{});
+	using QMainWindow::QMainWindow;
 
 	void closeEvent(QCloseEvent* ce) override;
 
diff --git a/src/gui/DetachableWidget.cpp b/src/gui/DetachableWidget.cpp
index 85f9c5b2359..be952e33e95 100644
--- a/src/gui/DetachableWidget.cpp
+++ b/src/gui/DetachableWidget.cpp
@@ -25,7 +25,6 @@
 
 #include "DetachableWidget.h"
 
-#include <QWidget>
 #include <QCloseEvent>
 
 #include "GuiApplication.h"
@@ -33,11 +32,6 @@
 
 namespace lmms::gui {
 
-DetachableWidget::DetachableWidget(QWidget* parent, Qt::WindowFlags f)
-	: QWidget{parent, f}
-{
-}
-
 void DetachableWidget::closeEvent(QCloseEvent* ce)
 {
 	if (windowFlags().testFlag(Qt::Window))
diff --git a/src/gui/DetachableWindow.cpp b/src/gui/DetachableWindow.cpp
index 33e0970c520..d86ac9447dd 100644
--- a/src/gui/DetachableWindow.cpp
+++ b/src/gui/DetachableWindow.cpp
@@ -25,7 +25,6 @@
 
 #include "DetachableWindow.h"
 
-#include <QWidget>
 #include <QCloseEvent>
 
 #include "GuiApplication.h"
@@ -33,11 +32,6 @@
 
 namespace lmms::gui {
 
-DetachableWindow::DetachableWindow(QWidget* parent, Qt::WindowFlags f)
-	: QMainWindow{parent, f}
-{
-}
-
 void DetachableWindow::closeEvent(QCloseEvent* ce)
 {
 	if (windowFlags().testFlag(Qt::Window))
diff --git a/src/gui/MixerView.cpp b/src/gui/MixerView.cpp
index 5e0e82d1e8f..9cf9fa53fdf 100644
--- a/src/gui/MixerView.cpp
+++ b/src/gui/MixerView.cpp
@@ -163,6 +163,15 @@ MixerView::MixerView()
 					this, SLOT(updateFaders()));
 
 
+	// adjust window size
+	layout()->invalidate();
+	resize(sizeHint());
+	if (parentWidget())
+	{
+		parentWidget()->resize(parentWidget()->sizeHint());
+	}
+	setFixedHeight(height());
+
 	// add ourself to workspace
 	QMdiSubWindow * subWin = getGUI()->mainWindow()->addWindowedWidget( this );
 	Qt::WindowFlags flags = subWin->windowFlags();
@@ -170,6 +179,7 @@ MixerView::MixerView()
 	subWin->setWindowFlags( flags );
 	layout()->setSizeConstraint( QLayout::SetMinimumSize );
 	subWin->layout()->setSizeConstraint( QLayout::SetMinAndMaxSize );
+	subWin->setFixedHeight(subWin->height());
 
 	parentWidget()->setAttribute( Qt::WA_DeleteOnClose, false );
 	parentWidget()->move( 5, 310 );
diff --git a/src/gui/SampleTrackWindow.cpp b/src/gui/SampleTrackWindow.cpp
index e2beda7e21f..f76cb8a211d 100644
--- a/src/gui/SampleTrackWindow.cpp
+++ b/src/gui/SampleTrackWindow.cpp
@@ -160,6 +160,15 @@ SampleTrackWindow::SampleTrackWindow(SampleTrackView* stv)
 	flags &= ~Qt::WindowMaximizeButtonHint;
 	subWin->setWindowFlags(flags);
 
+	// adjust window size
+	layout()->invalidate();
+	resize(sizeHint());
+	if (parentWidget())
+	{
+		parentWidget()->resize(parentWidget()->sizeHint());
+	}
+	setFixedSize(size());
+
 	// Hide the Size and Maximize options from the system menu
 	// since the dialog size is fixed.
 	QMenu * systemMenu = subWin->systemMenu();
diff --git a/src/gui/SubWindow.cpp b/src/gui/SubWindow.cpp
index bcd7fe59cfd..d22a337bf7b 100644
--- a/src/gui/SubWindow.cpp
+++ b/src/gui/SubWindow.cpp
@@ -252,10 +252,24 @@ void SubWindow::setBorderColor( const QColor &c )
 
 void SubWindow::detach()
 {
+#if QT_VERSION < 0x50C00
+	// Workaround for a bug in Qt versions below 5.12,
+	// where argument-dependent-lookup fails for QFlags operators
+	// declared inside a namepsace.
+	// This affects the Q_DECLARE_OPERATORS_FOR_FLAGS macro in Instrument.h
+	// See also: https://codereview.qt-project.org/c/qt/qtbase/+/225348
+
+	using ::operator|;
+#endif
+
 	if (isDetached()) { return; }
 
-	auto pos = mapToGlobal(widget()->pos());
-	widget()->setWindowFlags(Qt::Window);
+	const auto pos = mapToGlobal(widget()->pos());
+
+	auto flags = windowFlags();
+	flags |= Qt::Window;
+	flags &= ~Qt::Widget;
+	widget()->setWindowFlags(flags);
 	widget()->show();
 	hide();
 
@@ -264,10 +278,24 @@ void SubWindow::detach()
 
 void SubWindow::attach()
 {
+#if QT_VERSION < 0x50C00
+	// Workaround for a bug in Qt versions below 5.12,
+	// where argument-dependent-lookup fails for QFlags operators
+	// declared inside a namepsace.
+	// This affects the Q_DECLARE_OPERATORS_FOR_FLAGS macro in Instrument.h
+	// See also: https://codereview.qt-project.org/c/qt/qtbase/+/225348
+
+	using ::operator|;
+#endif
+
 	if (!isDetached()) { return; }
 
 	auto frame = widget()->windowHandle()->frameGeometry();
-	widget()->setWindowFlags(Qt::Widget);
+
+	auto flags = windowFlags();
+	flags &= ~Qt::Window;
+	flags |= Qt::Widget;
+	widget()->setWindowFlags(flags);
 	widget()->show();
 	show();