All dark beers have fizzy, dissipating head

I've made about 11 all grain beers now and I have kegged most of those. They all have a good, foamy head that usually leaves some lacing until the end. The exception is any beer I've made with dark malts. A stout, an attempted Smithwick's clone and an English brown using chocolate malt. These have a thin, fizzy head like a can of pop that disappears in seconds. What could be the cause of this? I carbonate everything at about 12 psi, and while it's fine for my other beers it seems to be problematic for these ones.

Am not sure, I notice no difference using darks malts on head formation and retention.

One idea for you to try might be to add a lb. of wheat malt to the beers that you have having trouble with - the higher protein content in wheat malt assists in head formation and retention, I'm told.

Could be a water problem.

Are you not using finings in your dark beers? Fine particulates in suspension will cause rapid head dissipation.

Thanks for the replies. I'm thinking that it may be my water. There's a subtle, odd flavour in all of my dark beers also that is not there in pale ales and other lighter beers.