unexpected staging order change

staging order of an engine changed from last stage to first stage after ONLY changing the length of a solid booster nosecone. I do not know whether or not y'all will consider this a bug. I could understand the staging order changing if I added an engine or a booster or something affecting how the stages would be ordered. But the ONLY thing I did in an edit session was to lengthen a nose cone thinking to gain a little time on one of the challenges with a little less friction with the atmosphere.