Site Error / Bug Certain symbols break chat messages when editing

[Sophie 24,410]

If you write a message and then edit it, anything after the & gets removed. 

For example, I can write "M&S" it will show fine, but if I then edit the message nothing after the M will be saved 

Edit - if I type "M+S" instead I get "M S" everything after is still there this time but the + is replaced by a space

Edit edit - <> is broken too. Could this be related to XSS prevention and &lt/&gt? 

Edit edit edit - %^~|[] {} @#*- =()_£"':;/ all work fine, I've only found issues with <>& and +