Can anybody explain to me why the following is happening?

I sprayed my M10 with Polly Scale flat coat yesterday to seal in some oil washes and filters. While I have never had this problem with polly s flat before, it dried into a dull sheen. In other words, the finish is flat when it isn't reflecting light, but in direct light it has a little bit of a shine. Polly Scale flat never did this to me before.

I know its not a bad batch because I have had good results from this bottle just a week prior.

Can it be due to the humid weather we over here been having lately?

One possibility is inadequate mixing. Clear flat paint is clear gloss that has been modified with inert additives. which settle rather quickly. The top surface of the paint has a reduced amount of modifier which causes the sprayed film to be glossier than normal. You can try agitating the paint throughtly and spraying another coat perhaps on the bottom to see if it makes any difference.

High humidity generally extends the drying time and in some cases cause "blushing" which appears as a white cast.

I would tend to agree with other poster, I use it all the time, But really needs mixed alot. MAke sure you give it a good shake, just prior to puring into airbrush cup

ok, you guys were right. I shook it up really well and that did the trick

thanks