SO... Google led me to this site:
http://www.northwesternextract.com/manufacturing-of-soft-drinks/
Where the most relevant info seemed to be:
"The flavoring ingredients used in making soft drinks must be water soluble allowing them to completely disperse throughout the drink with no separation. Flavors are supplied in two forms:
Extracts The flavoring oils and compounds are dissolved in
alcohol and water. Normally this form of flavor will produce a clear type of soft drink. Examples are lemon-lime [Seven-Up type], ginger ale and cream soda.
Emulsions Using various types of
food gums, the flavoring oils are suspended in aqueous solution. Homogenization is used to stabilize the oil in water compound. The proportions and mechanics are critical in order to prevent the oil from rising to the top or settling to the bottom of the finished drink. Citrus flavored drinks such as orange and grapefruit use this system and produce a cloudy type drink."
Looking at my bottle of Zatarain's "Root Beer Concentrate" I see it lists a bunch of chemical stuff, "artifical and natural flavors," and alcohol.
Looking at my bottle of McCormick concentrate, it lists a bunch of chemical stuff, "natural and artifical flavors," and two different gums.
While this may suggest the two concentrates might behave differently, it seems proof on this thread has been conclusive that they both settle out.
Now that I have firm temperature control, I'm going to try another small batch. I'm going to probably do the double-extract version (i.e. malt extract AND root beer extract) and do everything I can to clean it up before bottling such as using whirfloc and a bit of time in secondary.
THAT SAID: my guess is it will still settle out. BUT, if I do use whrifloc and secondary in order to minimize the amount of non-root-beer-flavoring sediment in the bottle, I'm guessing a nice GENTLE back-and-forth rolling of the bottle before pouring will bring it all back into solution long enough for me to drink it.