Bug report: panel properties dialog crashes

["o.t" <o t altavista net>]

There's a bug in the Control Center in the panel properties dialog.
Steps to reproduce it.

1. go to the buttons tab.
2. disable tiles
3. try
4. revert
5. disable tiles again
6. try

Now the dialog will crash.

Second way to reproduce it.
1. go to the buttons tab.
2. choose another tile for "Normal Tile"
3. try
4. revert

First bug: "Normal Tile" won't show the old tile.
5. choose a tile again
6. try

Now the panel properties dialog will crash.