If you examine the HTML code as displayed it has a &lrm character before the number.
This is a HTML left-to-right-marker to distinguish the display from using right to left. Presumably, without this invoices would not display properly in some languages
In older version (21.3.61 for example) there is no &lrm character
Lubos recently announced changes in how RTL text was displayed, so perhaps it is because of this
Wrong numbers direction in RTL languages - Manager Forum