I’m an user of the Italian forum and I spend lot of times trying to solve this issue.
Finally I discovered that with ZS 3.2.1 the problem is solved, but it’s necessary to use the most recent kernel 3.4.90-ZS
Infact with the “standard” kernel 3.14.21-ZS (delivered with ZS 3.2.1) this issue was still there.
By default the ZS image contain kernel version 3.14.21-ZS, as far as I know it’s necessary an active subscription to upgrade ZS 3.2.1 with Kernel version 3.4.90-ZS.
Hope it helps