NO, these leaks shouldn’t happen!
They didn’t occur in V 2.7 (or were fixed) but were re-introduced in early incarnations of V3. However, after I reported the leak (see: URGENT - NEW IP Leak (AR 750S) - #12 by glitch) they were fixed straight away (at least for the AR750S).
Can you upgrade to the latest test build and see if the leak persists.
If not, I posted a fix in this link (disabling Masquerading on the WAN interface):
Firewall Settings & Internet Kill Switch / Auto-Force VPN