Top layer cannot be renamed, it continually gets named back to Top Layer.
To reproduce: rename it, save the file, exit, restart viking, load the file.
Agreed - good spot.
Actually the 'top layer' name never gets saved to the viking file, thus on loading it is always initialised to 'Top Layer'.
Fixed in af39a781e3dc046abc3935e684bcef8b25042570
Top layer's name is no more editable.