#118 [external] when `ref`s are externalized, they are not updated when the original picture changes

[Stefan Pinnow]

Is it a bug that an externalized \ref figure is not externalized again when the original plot has changed? Can this be "forced" by somehow adding a dependency to the \ref?

This question was asked at http://tex.stackexchange.com/questions/297792/pgfplots-external-crossref-updates where you also find a MWE.