[Therion] White space along survey lines

Hello, Can someone help me with following problem: Survey lines in sketches (not in scraps) bring a white "channel" with them. I.e., white space along the survey lines. The white space makes the sketch beneath partly invisible. See picture. It appears that the white "channel" is derived from LRUD data, because if I omit the LRUD data, the white channel disappears, the survey line displays nicely. I looked at the definitions of l_survey_cave_SKBB and l_survey_cave_UIS (which one is used for symbol set AUT?) but have no idea how to redefine them to ignore LRUD. Michael.