I have found it likes to crack(Elm and many other woods bark is weak in tension) if its strained enough. It might even start splinters in your bow. I blew up an elm sapling bow not too long ago doing that.
I'm not gonna say your wrong about that because I haven't used it but I've seen people back bows with birch bark so why do you say that ?
If you don't remove the bark(keep bark intact) it does it.
also the bark is probably not as strong in tension as the wood lengthwise, and if you leave it on the bow it often will crack and cause problems. I mean literally cutting the tree, not debarking it, and letting it dry, not touching the bark, then making a bow without removing the bark. It will likely crack. If you take it off and glue it on... I dunno what would happen.
Now with wild cherry, its a whole another story