A snippet isn't going to help.
This sounds like an array misbehaving somewhere, resulting in a memory location being overwritten, and it happens to be part of the memory that makes the display map. The problem can either be in the display routines/library (somewhat unlikely) or (more likely) you have a problem with an array going out of bounds elsewhere in your code. Apart from an array issue it can also be something more complex such as wrong use of a memory pointer or a problem with malloc(), but an out-of-bounds array operation is the more likely cause.