The washes can go glossy. It can depend on a lot of things but I'd say the two most common reasons are whether it's been watered down or not and the thickness of the layers. It's happened to me with several different washes but don't despair it's not an issue.
Firstly make sure prior to painting you give the pot a good shake.
Secondly water it down or use a matte medium and apply thinner coats. Build your wash layers up. That way you get smoother transitions and you avoid a glossy finish
This should rectify the problem, however, if you find that it is still going glossy use your favourite brand of matte varnish and just coat the entire model. That will protect it while you game and sort out the gloss finish for you.
Hope this is a little helpful,
u_m