OK here's a down and dirty solution. What you are experiencing is called
"blush" in auto paint terminology. Lacquers blush when there is too much
humidity. Painting a car with lacquer in on a rainy day is disaster.
There is a solution when you just have to do it.
I am including a couple paragraphs from a book I wrote a few years ago.
It is about auto painting, but I found it worked when painting
polyurethene on wood. With a minor experiment, you may find it works
with stain. I also included a paragraph on "fish-eye", I hope this
helps. For wiid working, I would measure a teaspoon of Retarder to a cup
of stain, and try it on pine.
In highly humid areas or on rainy days, lacquer will show
moisture in the paint finish. This is called "blush", and will
show as a white area, and can make a paint finish appear
blotched with color variation. The better the grade of thinner,
the less chance for blush. The only remedy for a blushed finish
is refinishing unless you catch the blushing immediately. Blush
can be eliminated by adding "Retarder" (buy at auto paint supply) to the
mixture of paint and thinner in the spray cup. A little retarder goes a
long way. It is "chemically hot" lacquer thinner.
Essentially it turns cheap thinner into a slower drying medium
thinner, which allows time for the moisture to rise out of the
paint. Retarder will raise a medium thinner to a good thinner
grade for drying purposes. Retarder is not recommended for use
on every paint job because it eats into the previous paint and plastic
filler, raising imperfections where they wouldn't normally show.
When blush begins to appear, I add 3 oz. of retarder to each
quart of thinned paint in the cup. It is advisable to wait for
several minutes between coats of paint to see if blush will
reappear. If it does, you may want to add another ounce of
retarder to the paint cup, or wait for more ideal painting
conditions. If blush appears after the final coat of paint,
spray a mixture of 80% thinner and 20% retarder quickly over the
entire surface. Overlap onto the older surface. This will
assure a good blend, it cleans the spray gun, and helps
eliminate blush. Remember, if blush is persistent, you have the
option of stopping until a less humid day.
When you have finished painting, return the paint remaining in
the spray cup to the can. Avoid problems, DO NOT return paint
with retarder to the can.
Painters occasionally rely on an additive called fish-eye
remover. It is usually packaged in 4 ounce and 8 ounce plastic
bottles with pump tops. This product is an additive that only
requires one to four squirts of liquid in an entire quart of
thinned or reduced paint to do its job. Fish-eye remover
eliminates spots in the paint which resemble fish eyes. The
surface will show circles like oil drops on water, and unless
corrected, the paint finish will be ruined. The condition is
caused by oil vapor in the air (from spraying a silicone lubricant or
exhaust fumes), finger prints, contaminated paint, and dirt.
At the first indication of fish-eye, the painter adds one to
four squirts of fish-eye remover to his paint cup, and continues
spraying. Fish-eye remover will retard the hardening process
and increase flow out, which helps remove the fish-eye condition.
Some painters use the product in every cup of paint they
spray, as insurance against fish-eye. I don't recommend doing
this, because it changes the properties of the paint, and you
may not get uniform results in color and flow out.
Once fish-eye remover is used, continue using it for the rest of
the paint job, or the fish-eye remover may cause a fish-eye
condition of its own. Use fish-eye remover in both acrylic enamel
and acrylic lacquer. Follow the directions on the bottle
label. Fish-eye remover sold in a plain bottle without
directions or without a label has been transferred from a name
brand bottle, and could be contaminated or diluted.