CC controller data not overwriting.

[Steveau]

I've noticed a new unusual behavior recently, I probably have inadvertently changed a setting, but it's got me stumped.

After recording a Virtual Instrument, say Spitfire violins, I'll go back and write the CC data from my midi controller for CC 11 and 1, and maybe repeat that until I get it right,

and I'll use "write" mode for that track and keep it on Sound on Sound recording, as well, otherwise the notes would be erased,

and until recently it would overwrite any previously CC data and substitute  my new CC data, 

now I can only record on top of previously recorded CC data, and the resulting buildup is an up and down jerky mess.

Ideas?