post update chunk spawning totally unrelated to chunks spawned in other versions.

What I expected to happen was that after updating, When I went around my favourite world (which I have put a lot of work into) to do mapmaking, that new and interesting chunks would spawn regularly.

What actually happened was the chunks spawned, but they had no relation to the older chunks. For instance, a flat desert biome came to an abrupt end at a stone wall, which was actually the 'underground' depths of a new roofed forest biome. further along oceans suddeny transformed into extreme hills, and desert villages were halfway in desert, the other half in grassy plains. please help! and if you guys are feeling generous, make a way to delete and regenerate chunks so that my, and other player's favourite worlds are not in chaos.

P.S in some of the attached pictures you will notice that I tried to cover up the problem with some walls I constructed, as an "edge to my kingdom", but this soon become boring and I stopped.

PPS if you like I could email the map file to you.
Steps to Reproduce:
1. Put a step by step guide on how to trigger the bug here
2. ...
3. ...