psfred... Do you use foundation or do you let the bees build their own.
When using foundation, the bees tend to attach all the way down the sides and across the bottom bars, and as you said, the comb is strong enough to hold everything together. Without foundation, I find that they tie the comb sometimes in the center, sometimes 1/2 way down the sides, but rarely all the way down the sides and across bottom, as they do with foundation. This also helps to strengthen what ever joint is used.
I use the standard 2 dado cut, divided bottom bar, separation hasn't been a problem. If a problem is observed it may also be a result of bee space not being correct.