Peculiar issue with powershell Hashtable and array

Apparently a Powershell array holds only object pointers if a variable is added to it, so you have just added two references to a single object into your arry. To clarify, after your operations this statement:

$arry[0] -eq $arry[1]

will return true. To remedy, you should use clone() function to create an entirely new and independent object from $Msg, so that any modifications will not alter the object you've stored in your array.

$arry = @()
$Msg = @{Body="This is a Sample Message";}

$Msg.BrokerProperties=@{}
$Msg.BrokerProperties.Label= "Msg1"

$arry += $Msg
$arry | ConvertTo-Json    # 1st Result

$Msg=$Msg.clone() # create a new copy
$Msg.BrokerProperties.Label= "Msg2" # alter new copy

$arry += $Msg

$arry | ConvertTo-Json # get two different tables in array

EDIT: In your case, you have to clone BrokerProperties as well, because it is also a hashtable, and cloning an upper level $Msg results in two different objects which contain links to a single nested hashtable. So, in order to receive a completely different object, you have to do a deep copy of your hash table.

$arry = @()
$Msg = @{Body="This is a Sample Message";}

$Msg.BrokerProperties=@{}
$Msg.BrokerProperties.Label= "Msg1"

$arry += $Msg
$arry | ConvertTo-Json    # 1st Result

# $Msg=$Msg.clone() this is not enough!!!
$memStream = new-object IO.MemoryStream
$formatter = new-object Runtime.Serialization.Formatters.Binary.BinaryFormatter
$formatter.Serialize($memStream,$Msg) # serialization makes a string out of an object's structure
$memStream.Position=0
$Msg = $formatter.Deserialize($memStream) # deserialization makes a completely different object
$Msg.BrokerProperties.Label= "Msg2" # and now changing the nested hash table won't change the old one.

$arry += $Msg

$arry | ConvertTo-Json # get two different tables in array

On a side note: If you are creating multiple objects based on the same "template" object, you don't need to serialize all the time, just keep the references to $memStream and $formatter (one memory stream per object to deep copy, one formatter per script) and just call $memstream.position=0; $formatter.deserialize($memstream) to receive another prepared copy of the same object previously serialized.