If you use the Scroll Exporter app by K15TK15t, Scroll Exporter takes control of the numbering. This behavior is implemented in consultation with K15t.
Not sure if you are using the default Confluence exporter or the Scroll Exporter?
If you don't do not see an icon next to the Export menu item, you are most likely using the Confluence export.
This behavior was introduced in Numbered Headings version 4.0.6.