Wandering Trader Still Spawning

The gamerule doMobSpawning is set to false. However, the wandering trader has still spawned. Whilst this is not a massive issue, it does make mapmaking difficult, as this trader could spawn.

What I expected to happen was...:
The wandering trader would not spawn.

What actually happened was...:
The wandering trader did spawn

Steps to Reproduce:
1. Set gamerule doMobSpawning to false
2. Wait for the wandering trader to spawn