The bug is as the title says. It seems to be caused by a wrong scope for the TradeLicensesMax stats for the TradersTrait1 trait in the CultureTraitDefs.xml file.
Stats for the trait as found in the CultureTraitDefs.xml file.
<Stats>
<EffectType>TradeLicensesMax</EffectType>
<Scope>Global</Scope>
<Target>
<TargetType>Faction</TargetType>
</Target>
<BonusType>Flat</BonusType>
<Value>1</Value>
</Stats>
Changing the Scope to nothing (which implies Local scope) resolves the issue.
<Stats>
<EffectType>TradeLicensesMax</EffectType>
<Scope></Scope>
<Target>
<TargetType>Faction</TargetType>
</Target>
<BonusType>Flat</BonusType>
<Value>1</Value>
</Stats>
