Somewhat normal, yes. Think of it this way. Common duct system between the 2 AC's. Rear AC running, air goes through the duct, into the discharge ducting of the front AC, through the cage fan, through the coils and out the intake. Nothing really to stop the air from going that way, unless front is on as well. Shouldn't be any huge amount of air, but a little no doubt will make it through there.
John and Rebecca Dickson
Emma-7 / Little John-5 / Iva-1
Full Timing Again, Rev B
2013 Ford F-350 Lariat CC LB PSD
2015 SOB TT - With OC's Awning Poles (#8)
At least in Heaven, RVs will be perfect, and I won't have to keep fixing them.