Which of these cases is working as intended, I wonder?
My brother and I often duo, so we were keen on the introduction of Level Pacts. We made two sets of Pacted characters, which I'll call PactHeroA & B, and PactVillainC & D.
We deactivated our accounts at the same time just before Christmas last year, and reactivated them at the same time at the end of April. At no time was one account active while the other was inactive.
A couple of days after reactivation, my brother logged in on his own with PactHeroA. He didn't do anything with them, just looked them over, and moved them to a new location before logging out again. PactHeroA didn't gain any XP, and didn't see any messages relating to the Level Pact. The day after that, I logged in, on my own, with PactHeroB, and immediately got a message saying the Level Pact had been broken. As both characters were over Level 5, there was nothing we could do, other than bug report/petition it.
Following this, we logged in simultaneously with PactVillainC and PactVillainD. Both characters were, and still are, in their Level Pact.
Again, both of our accounts were deactivated, and reactivated, at the same time. Neither account was ever active while the other was inactive. Each log in described above was the first one for that character after reactivation of the account. One level pact broke when the characters logged in separately, the other pact still stands.