an observation:
my Rebel always picks the widest possible aperture when I have any Sigma or Tamron lens on it
with this Canon lens it picks all sorts of apertures. do you think maybe there is some kind of compatibility issue with aftermarket lenses?

because it was a new lens, I was trying all sorts of modes, and it picked all sorts of settings, as you'd expect, but with my Sigma no matter what mode I'm in it goes straight for the lowest available aperture. it only comes off of 2.8 if I force it to.

I've had a few Tamrons and Sigmas, and all of them have tended to simply go to the widest aperture. and on three bodies, I was thinking it was about the aftermarket lenses. I've had 2 T2i's and 1 T5i.

I've had:
1Sigma 18-200 new
1Sigma 17-50 new
2 Tamron 28-75's used, one refurbed
1 T2i new, 1 used
1 T5i new

now that I think about it, I have a Canon 50 1,8 that also tends toward 1.8 every chance it gets. I assumed it's just how they were set up, it's this 18-135 that's doing all sorts of things.

here's another photo out of the 18-135. it picked F 10 and ISO 400 with the flash, rather than something wider and a lower ISO. which is a bummer, I wanted to see what it looked like as wide as it would go to see how well it would do in a pinch doing portraits. this is just a bit too high in aperture. 

I agree that it is a hell of an overall carry around lens. Your shots here show that.
Would I choose it for intentional portraiture? No but that doesn't mean you still won't get the occasional stunner out of it.
It is just SO damn versatile that if you own one, it's hard to get rid of.   You'll probably have to pry mine out of my cold dead hands.
Heading to Florida in 2 days and I will have the 70-200 on my 70D but the 18-135 on my 40D and I think they will both be used equally due to some of the localities we will be hitting up.
BTW...when those kids get older in baseball, the action will start to get faster and faster. If you plan on shooting much sports (for example, at high school or above), you better find yourself a quick lens.  Nothing beats a quick lens to freeze that action at 2nd base (one of the hot spots for action photography).  THAT is when it gets fun...getting the ball in mid air as the runner approaches second on a steal attempt. Or mid play of the defense turning two. Good times!