Hi,

if you use an in-between target blend shape it should sort out your problem.

In a nutshell you should have 2 target blend shapes, full blink and half blink. Select the half blink, Ctrl select the full blink and finally Ctrl select your model. Now create your blend shape makng sure that the In-between box is checked in the Create Blend Shape Options.

I hope that makes sense,

Mat.