This is related to bug 51293, bug 61323, and the general bug 38129:

The alignment options in the media dialog's advanced settings are:

Left
Center
Right
None

It is the convention to not specify the alignment when choosing the default, mostly to avoid needless clutter in the wikitext. If the default is right (or left), and the user chooses that default, then VisualEditor should not add "right" but instead should leave the alignment setting empty.

Version: unspecified
Severity: minor