The pool statistics "Available" shows wrong value after fill pool in EAP 6

Issue

The pool statistics' "Available" shows wrong value (one less than "max-pool-size") after fill pool.

For example, min-pool-size=5, max-pool-size=10 and prefill=true are set to datasource configuration:

  <pool>
      <min-pool-size>5</min-pool-size>
      <max-pool-size>10</max-pool-size>
      <prefill>true</prefill>
  </pool>

Then, when checking pool stats via CLI after JBoss start-up, the results shows the following:

[standalone@localhost:9999 /] /subsystem=datasources/data-source=ExampleDS/statistics=pool/:read-resource(recursive=false,proxies=false,include-runtime=true,include-defaults=true) 
{
    "outcome" => "success",
    "result" => {
        "ActiveCount" => "5",
        "AvailableCount" => "9",
        "AverageBlockingTime" => "0",
        "AverageCreationTime" => "3",
        "CreatedCount" => "5",
        "DestroyedCount" => "0",
        "MaxCreationTime" => "4",
        "MaxUsedCount" => "1",
        "MaxWaitTime" => "0",
        "TimedOut" => "0",
        "TotalBlockingTime" => "0",
        "TotalCreationTime" => "17"
    }
}