Left panel: EXTraS/STV light curve of the star HD 283810 with uniform time binning (500 s). A large flare is seen in the second half of the observation. The tail probability of a fit with a constant model is < 10⁻²⁵. The flare is missed by the 4XMM variability analysis because it occurred outside of the GTI (see right panel). Right panel: background light curve of the same observation, taken from the 4XMM products. All observing times with a background rate exceeding the threshold marked by the blue line are rejected. The time interval of the flare (see left panel) is therefore excluded.