I am afraid, I uninstalled the AnchorDocking-thing for the second time. :'(
It is a pity, because I liked this docking.
You only need to reset the values. In your lazarus config dir you find a files called enviromentsoptions.xml back this up and go inside of Lazarus , select the splitter and click rigth, the activate 'show header'. Maybe you have mishit this.
Edit: It looks like indeed a bug. If you hit this, you will never can go back.
Close Lazarus. Open the enviromentsoptions.xml and search for a line with "Settings ShowHeader="False"" remove the ShowHeader="False" or change it to True. After reopen the dockings will be shown.
</Item1>
</Item1>
</Nodes>
</MainConfig>
<Settings ShowHeader="False" SplitterWidth="3"/>
</AnchorDocking>
</Desktop2>
</Desktops>
</CONFIG>
The SplitterWidth is the size of the splitter, normal = 4 i have changed this to 3
Backup: Go in Lazarus to menu Tools->Desktops... there is a Export Button - use this :-)
To avoid unwanted changes. Open the dialog and remove the autosave option. You can always store your changes with Save active desktop as.. and give the same name as before