A while ago I asked why some words that were marked to be added to my personal dictionary were not added, and were highlighted for correction each time I ran the spelling checker. I've isolated the cases where this occurs.
This happens with only collective possession terms; that is, those with the possessive apostrophe to the right of the terminal 's.' For example, the LyX spell checker (perhaps a plug-in?) will accept "community's" and "communities", but not "communities'" (the latter referring to a trait found in all communities.) Perhaps this can lead to a fix for the next release. Regards, Rich