Cannot enable all the available syntaxes from the administration

Go to the Wiki Administration > Editing > Syntaxes section and uncheck all disabled syntaxes. Then edit a wiki page using the Wiki editor and check the syntax drop down from the Document Information panel. Instead of listing all the enabled syntaxes it lists only "XWiki 2.1". If you put the following script in a wiki page:

{{velocity}}
$services.rendering.disabledSyntaxes
{{/velocity}}

you'll get:

[Plain 1.0, XML based XDOM current, Markdown 1.2, XHTML 1.0, XWiki 2.0]

although we previously unchecked all of them from the list of disabled syntaxes.

The problem seems to be in DefaultExtendedRenderingConfiguration#getDisabledSyntaxes() which handles the empty list (our case) as if the configuration is missing and falls back on xwiki.cfg

// If not found, look in the xwiki cfg source for a xwiki.rendering.syntaxes property
if (disabledSyntaxesAsStrings == null || disabledSyntaxesAsStrings.isEmpty()) {