Hmm... could you find the value that gives the dimensions of the lowest of the 2 sidebar SHP files? If it's extended to the bottom, a simple edit of the SHP file (filling the bottom) might fix the sidebar refresh error.
I think that I solved that. In attached file is a modified shape (original is in updatec.mix). I do not know what is the best way to incorporate it into the game. During testing I replaced it within the original mix file. You also need to apply following modification because the game used too small buffer so the sprite was not working correctly.
#Allocate buffer bigger than 40000 pixels
000443E5: 40 FF
000443E6: 9C FF
000443E7: 00 F0
000443EA: 40 FF
000443EB: 9C FF
000443EC: 00 F0
#Allow width * height to be bigger than 65535
00056010: 66 8B
00056011: 8B 55
00056012: 55 76
00056013: 76 90