I'm going "duh" at most of your excellent answer--I should have figured out the acronyms, at least. Retired 8th grade teacher, though, so it's impossible for me to be genuinely embarrassed. ;-)
Thank you for the detailed explanation. I was a computer teacher and I've been a dedicated geek since the early 1970's. I would love to use FTMM, if only for its reports which I find much more attractive Reunion. Plus I genuinely enjoy working with FTMM's interface.
Unfortunately, FTMM has consistently given me problems to the point that I can't trust it: reports with missing or incorrect information; unsorted children; unexpected crashes; corrupted databases. Tony and I (among many others) tried as hard as we could to make it work with no success.
It's hard to understand why FTMM operates well for some and not others--even taking so many different configurations into account. My computers are kept in tip-top shape; HDs aren't too full; I regularly clean out old files, run utilities, update all software, etc. So far I've removed FTMM preferences, uninstalled the app and its related files, started new trees from scratch--all multiple times on both MBP and the 27" iMac--and nothing seems to get rid of a myriad of problems.
When I buy a new app, I expect it to have growing pains. As much as anything, though, Ancestry has completely lost my respect for its initial false report that FTMM was built for Mac from the ground up, for its lack of accountability and for (I assume) only the one update.
My hat is off to all of you who can make FTMM work--I would love to be counted among you but time is too precious to spend any more of it on FTMM. ;-)