Bruno:
sería posible disponer de la propiedad TSplitter:ResizeStyle, para controlar mejor el redimensionado de los controles que contiene el Splitter.
EN C++ Builder 6, tiene estos estados:
rsNone Moving the splitter with the mouse has no effect.
rsLine A line is drawn indicating the new position of the splitter that would result if the user released the mouse at the current position. The splitter does not actually move and no controls are resized.
rsUpdate The control against which the splitter is aligned is resized based on the current mouse position, and the splitter is moved to that position.
rsPattern A pattern is drawn indicating the new position of the splitter that would result if the user released the mouse at the current position. The splitter does not actually move and no controls are resized. This is the default value for ResizeStyle.

El estado rsLine, lo veo muy interesante, ya que solo se redimensiona cuando se suelta el ratón , mientras tanto solo se dibuja una linea donde quedará el Splitter al soltarlo. Es como lo hace el Explorer.exe, de esa manera creo que se evitan redimensionados cada vez que se desplaza un pixel el Splitter y desaparen los parpadeos propios del redimensionado.

Una sugerencia.

Un saludo.
Vïctor