Could I really lose a whole gallon to my hops?

It appears that my hops ate a whole gallon of my beer.  Here are the details:
Pre boil volume: 6.75 gallons (1.064 gravity)
90 minute boil with 13 percent evap rate.
finishing volume only 4.5 gallons (1.080 gravity) (instead of 5.5 at 1.080)
According to beersmith I should have had my target 5.5 at 1.080.  I know it can't just be a higher evap rate, because then my gravity would have been higher (1.096)
I had about 5 ounces of hops (4 of them leaf, 1 of pellet)
I have negigeble dead space in my kettle.  I just can't think of where my extra gallon went (I mourn the loss of beer!)
I am new to AG brewing, so maybe this is common, but I haven't read/heard anything about this size of loss during the boil.
Any ideas?
Steve

Are you sure that you used the correct amount of water for mashing and sparging?

If you lost that much in the boil your OG would not always be more than expeted if you are getting poor eff.

Lets start there.

Don

I calculate a 74% eff (17.4 lbs of grain, 6.75 gallons of 1.064 wort collected)
Either way, I know I had 6.75 gallons of 1.064 before the boil, and only 4.5 gallons of 1.080 after the boil.  I have adjusted gravities for temperature.
If I plug this into a boil off formula, it shows that I lost 22% per hour and that my OG would be 1.096!
If I play with the percent per hour boil off to get it to match my actual OG, it shows that I would be losing 13% per hour (reasonable) but that I would have gotten my target 5.5 gallons.
I am pretty confused as to what happened to my gallon.....
Thanks for looking at all of this.
Steve

Having just brewed a beer with a ton of hops, ok, only a pound, all whole hops, I can see maybe a half gallon, if everything worked against you, for your 4 ounces, but not more than that.

Fred