There is discrepancy in undertow schema definition of listener attribute 'max-header-size' default value here and ListenerResourceDefinition here.

Note: Default value in ListenerResourceDefinition java file was changed by this commit

These two default values should be unified so they match.

NOTE: I set GA as a target release as this is probably trivial change in Undertow schema definition which is better to do before GA as after that any change into schema is difficult.