Quite simply, if they wanted to prevent unsummoning then resummoning to get rid of effects, they should have had the effects continue their countdown while the pet is unsummoned, so in this case if the effect had a 10 sec countdown to a massive AoE and the pet was unsummoned, if it was resummoned any more than 10 secs later, the effect would be gone, but if it was summoned a second later it would still be there with one second less on it.