Humbrol and Tamiya Acrylic Spray Reaction?

[mick b]

Hi

I am currently building an old Tamiya motorised Sherman for my lad and have sprayed the main assemblies in Tamiya Acrylic Olive Drab from a can. It dried beautifully and chose to matt it down with a cheaper Humbrol Acrylic Matt Varnish Spray.

However despite vigourous shaking the varnish has a tendency to dry as a light grey on the green in some places and its not down to excessive build up as it happens after the first quick pass.

So has anyone else experienced this and do I need to fork out on the expensive Tamiya varnish to avoid a recurrence?

TIA

Mick