Up until the start of Alliance War Season 4, when you went to 'Join'/place your Alliance War Defense, whatever Mastery setup you had at that time is what was set/locked in for your 5 Alliance War Defenders.
I recently discovered that, as of AW Season 4, this no longer appears to be the case.
During our first Alliance War of Season 4 on 9.13.2018-9.14.2018, we noticed that our opponents had more defenders than usual with Suicide masteries on. We took note of which opponent player defenders had suicides on, so we'd know that their other defenders should also have suicides on.
However, when we reached the AW Boss (opponent player which had suicides on his prior defenders), we were surprised to discover no suicides on the AW Boss.
What this means is that it appears your Mastery Setup is no longer being saved/locked in for your AW Defenders when you hit "join"/place your defense. Your AW defenders mastery setups are now changing during war any time you change your masteries in real time (the way it normally impacts your attackers).
This change has a huge negative impact on Arena Grinders that usually place their AW defense without suicides on (locking in no suicides on defense), then turning suicides back on to do their arena grinds.
@Kabam Miike @Ad0ra_ Please advise if this change to how Mastery setups work for our Alliance War Defense is intended or if it is a bug.
FYI
@mutamatt @DNA3000 @DrZola