Thanks for the report.
This issue is close to this one https://github.com/plantuml/plantuml/issues/140
With last release (1.2018.10), you can add skinparam fixCircleLabelOverlapping true that somehow fix the issue :
@startuml
skinparam fixCircleLabelOverlapping true
node Proxy {
StreamDistributor - [Second Component]
}
@enduml
http://www.plantuml.com/plantuml/uml/1S512i903030UrwH3_Y7GZqA2ZsAXxGR9RX9bcnMAkBVEpFrfCYX5VfRh56GubFsMMAhVA6Lw_N3KQariHTc30OmBuotyFsBFrWocFGiFKFMaHvumll2crl1sRMviUK3_Z2nbQ7r0000