Why did mods not use the deleted subthread feature here?

[ClarkUSA]

Here, my reply to Prism's deleted personal attack was deleted separately from Prism's:
http://www.democraticunderground.com/discuss/duboard.php?az=show_mesg&forum=433&topic_id=777933&mesg_id=778161

I said simply, "How ironic that you say so." Nothing more. Why did mods choose to delete my reply to Prism separately as opposed to making both related comments part of a deleted subthread, given my relatively innocuous reply does not break any DU rules that I am aware of. I PM'd mods re: this discrepancy hours ago. They haven't changed it to a deleted subthread yet so that's why I am coming here. Perhaps they will do so soon and save you the trouble.

[EarlG]

1. He accused you of being a troll, you responded in kind

Both of your posts were deleted. It was not necessary to remove the subthread.

[ClarkUSA]

2. "in kind"? I beg to differ. I did not accuse Prism of being a troll nor did I personally attack him

I simply said one line, ""How ironic that you say so" meaning I thought he was completely wrong in his judgment of me, that I am the opposite of a "troll" given my intentions.

An ironic remark conveys a meaning that is the opposite of its literal meaning. So, in an ironic statement one thing is said, while another thing is meant.

http://hotword.dictionary.com/ironic

i·ron·ic ...

Poignantly contrary to what was expected or intended"

http://www.thefreedictionary.com/ironic

Based on these literary definitions of the adjective "ironic" please help me understand just how mods determined what I said was worthy of a deletion and on what grounds?

Does this deletion count against me? If so, what exact DU rule did I break so I do not fall foul of it again? Is "ironic" now a banned word at DU? Or perhaps mods do not understand the proper definition of the word. What did they think I meant? I believe this deletion was uncalled for.