Sheetmetal flange length driven by sketch constraint

Hi,

I'm testing out some ways to form sheetmetal parts using a master part and eventually a design table.

I have the master part inserted into another part and have created a sketch which pulls through the required values from the master sketch. The flange angle and length are then driven by the master part. The flange angle is working okay but when I edit the flange sketch to determine the flange length by constraining it to a line in the master part i get an error. The sketch looks okay and the constaint (pierce) works fine but when I exit the sketch the flange length comes up short. See pictures below:

1. Flange angle

2. Editing flange length by contraining to contruction line in master part. Length is correct.

3. Exit sketch. When SW builds the flange it is coming up short?????

I have no idea why???

Any ideas?

Thanks,

Ray.

SolidworksSheet Metal