Not sure if this has been reported (most likely has)
Spell Check gets a bit antsy with certain odd word combinations. for example, “I’ve always” gets the Spell Check response “I’ve always”.
It also did it with “come to” and “doesn’t it all”. With “doesn’t it all”, Scrivener is convinced I mean “tit”. 
I’ve noticed that the spell checker likes to point out doesn’t as incorrect, underlining th doesn’t portion. Also I noticed that sometimes the red underlining is off relative to the word position but I was unable to replicate it regularly enough to offer reproduction steps.
I’m also getting spell check errors such as “rous_first_d” is underlined in red when it is actually “disasterous first date.” Also “he_s” when it is “the sweater.” It’s annoying, but not detrimental.
I’ve noticed that the red underline for the spell-check function is offset about a quarter of an inch to the right of where it should be. this means that it only underline part of the word, and can be quite confusing.
This morning I was typing and saw the same issues that the other users reported. Then I found out how to turn off smart quotes. Since I had only typed a small section, I decided to go back and delete and retype the smart quotes and curly apostrophe’s with their straight counterparts. All of the spell checking underlines went away.
I did notice that it wasn’t every contraction. I’ve and I’ll seemed to have no issues.
I noticed a slight offset as well. I accidently wrote “their opponents” as “thier opponents” and the spell check underlined it as “thier opponents.” It was a bit confusing, until I read the few posts above.
Beta 1.2 is available for download and fixes this issue.
http://literatureandlatte.com/forum/viewtopic.php?f=32&t=9100