Hi,
Please see pics below of the mould and the part after infusion.
The mould has been applied 6 passes of easylease, 1 pass of wax and 1 mist of pva before laying fabrics.
All the timing between passes has been respected, and pva was left overnight to dry.
Composite spray glue from ec has been used to keep the fabric in place.
When it came to extract the part, some small areas detached as they should fine but the majority had the gelcoat stuck on it, as visible in the pic.
I was afraid of a long sanding job but tried first with a chisel and small strokes and with much relief chips by chips all the stuck gelcoat came away with leaving a glossy part surface.
My questions is:
- what could be the reasons why the gelcoat was so adhered (I use adhered and not bonded because with some mechanical force the gelcoat separated) to the part? 

Silicone or not, if epoxy gelcoat is fully cured, the reinforcement layers will not bond properly. I have made several mould from several different kinds of silicone without ever having a problem. This is not a general problem. At least not for moulds.