Do you mean the Notes widget?

I cannot reproduce in 4.7, can you provide more information:
- add a Notes widget, write some text 
- in a terminal type
kquitapp plasma-desktop
plasma-desktop 
in order to restart the plasma workspace.
Does the Notes restore its text?

I confirm this bug.

Each time I log in a single empty note appears on to my screen. 

I tried to do the procedure you talk about to provide some information, but I can't notice anything suspicious. Maybe I did something wrong, so here is what I did :
 - I create a new note for testing purpose with some text (i.e. "test")
 - I type kquitapp plasma-desktop on a terminal => all plasma widgets (including task bar where knotes is docked) disappear, but the new note widget left on screen.
 - I type plasma-desktop on a terminal => all plasma widgets are displayed back. A bunch of log message is also displayed on my terminal, but nothing seems related with this problem. Anyway here is a copy of what is displayed
===
QDBusObjectPath: invalid path ""
Connecting to deprecated signal QDBusConnectionInterface::serviceOwnerChanged(QString,QString,QString)
QGraphicsLinearLayout::removeAt: invalid index 0
plasma-desktop(15440)/kdecore (services) KServiceFactory::findServiceByDesktopPath: "systemsettings" not found
plasma-desktop(15440)/kdecore (KLibrary) kde4Factory: The library "/usr/lib/kde4/solid_hal_power.so" does not offer a qt_plugin_instance function.
QGraphicsLinearLayout::removeAt: invalid index 0
QPainter::begin: Paint device returned engine == 0, type: 2
QPainter::setRenderHint: Painter must be active to set rendering hints
QPainter::setPen: Painter not active
QPainter::setFont: Painter not active
QGraphicsLinearLayout::removeAt: invalid index 0
QPainter::begin: Paint device returned engine == 0, type: 2
QPainter::setRenderHint: Painter must be active to set rendering hints
QPainter::setPen: Painter not active
QPainter::setFont: Painter not active
QGraphicsLinearLayout::removeAt: invalid index 0
QPainter::begin: Paint device returned engine == 0, type: 2
QPainter::setRenderHint: Painter must be active to set rendering hints
QPainter::setPen: Painter not active
QPainter::setFont: Painter not active
QGraphicsLinearLayout::removeAt: invalid index 0
Invalid D-BUS interface name 'org.kde.plasma-desktop.PlasmaApp' found while parsing introspection
QPainter::begin: Paint device returned engine == 0, type: 2
QPainter::setRenderHint: Painter must be active to set rendering hints
QPainter::setPen: Painter not active
QPainter::setFont: Painter not active
QPainter::begin: Paint device returned engine == 0, type: 2
QPainter::setRenderHint: Painter must be active to set rendering hints
QPainter::setPen: Painter not active
QPainter::setFont: Painter not active
QPainter::begin: Paint device returned engine == 0, type: 2
QPainter::setRenderHint: Painter must be active to set rendering hints
QPainter::setPen: Painter not active
QPainter::setFont: Painter not active
QMetaObject::invokeMethod: No such method PlasmaApp::loadCommandLineOptionsForNewInstance()
setting locale to  "utf-8"  and encoding to  "utf8"

+ a bunch of data related to CWP plasma widget
===

I hope this may help...

I am confused whether you talk about the Notes widget or KNotes itself. The first reporter mentions KNotes but filed under Plasma

There are 2 different things:
- the Notes widget which is added via "Add Widgets..."
- the KNotes application which is a PIM application

Please add a screenshot so it's clear what you are talking about, thanks in advance.

Anne-Marie, Knotes, not the widget.

This was filed under the wrong product so reassigning.

*** Bug 230034 has been marked as a duplicate of this bug. ***

I got the same problem few months ago.

It has due to an old personnal script in ~/kde/Autostart/ who launch the command “knotes” on login.
Since KDE 4.6 or 4.7, Knotes starts alone on my computer. With my script, I had had “double launch”. It has misinterpreted and cause the creation of the empty note.

Maybe something like that?

Is this still valid for you with KDE 4.8.5 or 4.9.x?

Can't reproduce it in 4.9.0.

Thank you for the fast feedback.