Seems you have the same problem as me
During transfer from the dns host/slave combo to the slave somehow the zonefile get's corrupted / compressed in two lines.
I don't know if the script is causing it, or it gets compressed during ssh but the end result of your slave is the same, a servfail since it cannot read the "db.myexample.com" file.
I have a similar setup like you, one normal box 1 core 6gb memory and two smaller ones with 1 core and 1.7 gb memory for hosting the nameservers.
Sorry for not having an answer yet, still trying to figure out what is causing it :-)