Several AGNs have been reported to have ultra-high velocity (UHV) outflows (of order 0.3 ≳ ν/c ≳ 0.05) that are detected in their X-ray spectrum. Re-visiting these outflow observations reveal that the spectrum has changed along with the claimed outflows. The luminous quasar PDS 456 is the brightest AGN in which a UHV outflow has been claimed to be present in its grating spectrum. We report on an XMM–Newton observation of this source, as well as analysis of past observations, which reveal its variable nature and the variable nature of UHV outflows. In this object, as well as in a few others, repeated observations failed to reproduce the previous absorption spectra. This indicates that variability is common among the UHV winds. A discussion of the reality, significance, and the interpretation of the UHV outflow phenomenon is presented. If UHV outflows exist, they might be a transiting phenomenon, as indicated from repeated observations, and this has to be taken into account when studying the influence of these outflows on the surrounding galaxy.