Posting here to give you the infos i've got so far about changes in .mul files happened with patch 7.0.9.0 (aka High Seas Adventures)
I've been able to see something in the files using mulpatcher, but even it cannot open correctly them all
Art.mul
It has been extended again, up to 0xFFDB for sure (maybe 0xFFFF?)
Fiddler reads it like it's the OLD art file (0x3FFF limit)
mulpatcher displays it fine
Tiledata.mul
Like above, for sure
Anyway, Fiddler reads it up to 0x7FFF
mulpatcher instead reads it up to 0x225F
Multi.mul
It cannot be read anymore by Fiddler, probably because some multis is using new extended values.
Same with mulpatcher.
Animdata.mul
Fiddler completely fails to open it (probably due to the raised limit).
mulpatcher opens it successfully til 0x3FFF
Radarcol.mul
Opens correctly in Fiddler till 0x7FFF
Like supposed, the biggest "problem" should be Multi.mul, maybe along with Animdata.mul...
Hope you find this useful