I run into this all the time with my site's keywords.
If you go to Google and type in the various order of the keywords you will indeed get different results pages. If you go into Google Adwords Keyword Tool you will most likely see the exact same search numbers.
What does this mean? Google obviously recognizes that these are in essence the same keyword and report back search behavior appropriately. This of course takes us back the SERPs which will be different (although often very similar - and the 1 ranking will often be the same) which is clearly more explicit in displaying rankings.
One side note, I have noticed that plural and singular terms are often very different in search volume and SERPs - for example Blue Wide Widget vs Blue Wide Widgets. Here is a case were the intent would be the same (I would guess) but the user behavior must be so different that Google treats them completely separately.
My recommendation: You should be building a breadth of anchor text anyway so link using them all with a predisposition to point using the term that Google suggest defaults to. Hope the helps!
