[Plugin: WordPress SEO by Yoast] using the – symbol in keyword

i am having the following “problem”
this is my site
Yesterday i updated most of the pages (used all in one seo before) but when I enter a
keyword like “AH-1W Super Cobra”
it doesn’t recognize it in the Article Heading, and thus show a red “no” error.
I came across this problem wit a few other pages. like with those:
– F-117 A
– F-14
– Blackhawk MH-60L DAP

all those keywords use the – symbol and error on the heading part, but i got the exact same words and symbols

this problem also appears with abbreviations when you use something like this: D.A.P.

should I ignore the heading error??

http://wordpress.org/extend/plugins/wordpress-seo/