Could this be a timing problem on my initialisation?
most likely, the displays have two screen memory regions one for graphics the other for the normal lcd character display
at power up display is in lcd mode, the init routine sets it to graphics, lcds are slow to powerup they cannot be hurried.
if the display is written to before graphics mode is established then its possible some lcd chrs will be displayed accidently.
lcd chrs can only be cleared if the display is in lcd mode , graphic pixels can only be set in graphics mode
both memories are visible on screen no matter what mode is set.