Detail of the P branch in the Feros spectrum of HD 135230: observed (black dots and points), and after correction with TAPAS (green points and line, right scale au). There is a P Cygni pattern in all absorption features. The sign of the P Cygni changes along the spectrum. It goes to zero at 766.5 nm, then reverses its sign, when going from one doublet to the next. There is a line at 766.39 nm in the star spectrum (question mark), not corrected by the atmospheric correction, identified as an interstellar line of potassium at 766.4911nm.