No, to place orders in the match t complete them is not illegal.
In fact, that's the very reason the match was conceived in the first place: to facilitate the completion of orders, both buy and sell, that remained unfulfilled after the normal trading day, assuming that is the instruction and/or desire of whoever gave those particular orders to the respective broker.
All the match should be considered to be is a closing auction (for those who wish to participate.)
There's nothing insidious about it at all.
I have bought and sold shares in the match on many occasions, with absolutely no adverse outcome compared to my buying or selling of shares during the normal course of trade.
MSB Price at posting:
$3.54 Sentiment: None Disclosure: Not Held
A personalised tool to help users track selected stocks. Delivering real-time notifications on price updates, announcements, and performance stats on each to help make informed investment decisions.
(20min delay)