Stack tracks phase/panning issue

hello all. i am a moderately experienced Logic Pro user however i have a problem. i am used to creating summing stack tracks and everything seems to work fine until i act on the pan of a track contained in it. even though these are often mono tracks if i hard pan a track my correlation meter reveals inconsistency between the R and L channels, in solo and without sends or effects... the problem is clearly audible in headphones. in general, working with this approach i do not hear the clear separation of a hard panned track. does anyone know the problem? where am i going wrong? is there a way to faithfully sum tracks in bus groups? thanks and i hope i have asked the question in the right place and way.