I'm working with a 60 year old (at least) starter. I've been making
breads and rolls for years and just recently decided to try my hand at
sourdough.

While starting a firm sponge last night, I noticed the dough got more
sticky as the mixer worked it. Seemed as if there were lots of gluten
strands, but not enough flour. Is this normal?

I let it proof over night and then finished the kneading by hand and
adding more flour (as the recipe called for). I was able to get to the
"windowpane" stage, so I'm hoping things will turn out.

Any info (including "read the FAQ newbie") would be greatly appreciated.