No, it can't be responsible for that because it's not attached to simgraph_init nor any of its variables. It also does not change how the RGB555 is translated to system format. It does not even keep/save stuff in the memory (in an array), it simply calls get_system_color and the 8 bit palette and returns an RGB colour in system format.
And yes SDL1 works, the design was changed for it, and it was changed to be safer. Changed as I explained above.