In a survey conducted between 2011-12 of interstellar Na i D line profiles in the direction of the Vela supernova remnant , a few lines of sight showed dramatic changes in low velocity absorption components with respect to profiles from 1993-1994 reported by Cha & Sembach .
Three stars - HD 63578 , HD 68217 and HD 76161 showed large decrease in strength over the 1993-2012 interval .
HD 68217 and HD 76161 are associated with the Vela SNR whereas HD 63578 is associated with \gamma ^ { 2 } Velorum wind bubble .
Here , we present high spectral resolution observations of Ca ii K lines obtained with the Southern African Large Telescope ( SALT ) towards these three stars along with simultaneous observations of Na i D lines .
These new spectra confirm that the Na D interstellar absorption weakened drastically between 1993-1994 and 2011-2012 but show for the first time that the Ca II K line is unchanged between 1993-1994 and 2015 .
This remarkable contrast between the behaviour of Na D and Ca II K line absorption lines is a puzzle concerning gas presumably affected by the outflow from the SNR and the wind from \gamma ^ { 2 } Velorum .