[Yaffs] Performance of overwrite vs new file

I've run into an interesting performance issue that I
was hoping someone with more knowledge of YAFFS's inner
workings could explain rather quickly.

Essentially, I am observing that overwriting a file (1MB or so)
takes about 7 times longer than writing exactly the same file
under a new name.

This is using YAFFS1 on NAND with 512B pages.

Thanks for any insight.