Line Graph Re-sizing (all squashed)

[GandalfTheWhite]

I have a line graph that randomly squashes itself up, the Frame stays the same size but the Plot Area squashes up. There is no Auto-scale set anywhere and the data isnt changing. The Source Data however contains Blank cells and the graph will grow as data is added. Could this be the cause? If so is there a way round this (apart from Manually amending the data range each time).

Appreciate any help or advice.

Thank you