1) When I select 112th Rifle Division (marked as part of 24th Rifle Corps) it also highlights three divisions next to Belgorod, that are part of 24th Guards Rifle Corps. Surely this is a bug in highlight code, that checks only "numbers", not full unit identity (24th RC != 24th GRC).
2) When I select said division it also higlights two rifle brigades: the 129th in the same hex and the 42nd in another. It also works the other way round. Probably the corps was made up at that time from such units, so this may be historical but it does not work with the limitations in the engine.
First - it's not listed next to brigade's name that it is part of 24th Rifle Corps.
Second - by moving all three units to single hex and selecting "build up" button, the two brigades merge into "1st Rifle Division (24th RC)". This looks like a standard "2 brigades into 1 division" buildup, though it retains the "parent corps" information. It's impossible to rebuild the full corps now, as it only has two out of it's three components.
Third - it's possible to take one division of the 24th GRC and use it to build up 24th RC. So as the highlight code has a bug, so the buildup code has the same bug. It makes parts of 24th RC and 24th GRC interchangeable. Upon breakdown the division that was formerly part of GRC is now marked as part of RC.
To sum it up:
1) a bug should be fixed in highlight code and buildup code that allows to mix parts of parent units if their name is the same.
2) if a brigade is part of a corps (due to scenario designer making so) it must be marked as such in unit detail box and should allow proper buildup of said corps (unless it's impossible to do so - then, the scenario should be edited to not contain such 1 div + 2 brig corps).