MemchacheBucket Upsert method doesn't consider the expiration Timespan

This method

public IOperationResult<T> Upsert<T>(string key, T value, TimeSpan expiration)
{
return this.Upsert<T>(key, value, expiration.ToTtl(), this.GlobalTimeout);
}

use the following method

public IOperationResult<T> Upsert<T>(string key, T value, uint expiration, TimeSpan timeout)
{
return this._requestExecuter.SendWithRetry<T>((IOperation<T>) new Set<T>(key, value, (IVBucket) null, this._transcoder, timeout.GetSeconds()));
}

expiration param isn't considered. This cause the object to have infinite duration.