When a Java dependency behaves unexpectedly, the cause may be deeper than the application code calling it. This talk examines four real OpenTelemetry Java fixes involving thread-pool bounds, iteration and removal in a map used for asynchronous metrics, a mismatched Jaeger sampler configuration key, and sensitive values appearing in configuration errors. Each example illustrates a different debugging challenge and shows why resource limits, collection semantics, configuration paths, and diagnostic output deserve careful review. Attendees will take away a practical approach to investigating library defects and understanding how small implementation mistakes can affect larger systems.