Thanks for a clear answer to a very puzzling problem I had too.
This is not a bug, it's a feature
Looks like the beginning of a transitional period. Better live with 256 bits and set our Grub on a 256 bits ext3 filesystem.
The following is a fairly recent quote that further confirms this trend:
I was reading something, and came across this item in mandriva, someone else had referenced it re siduxhttp://wiki.mandriva.com/en/Docs/SysAdm
With Mandriva 2008.1, the format for representing files on disks has been slightly modified: 2008.1 uses inodes with a size of 256 bytes rather than the 128-byte inodes of earlier systems. That may create difficulties on multi-partition systems when booting from a non-2008.1 Linux partition (that still uses 128-byte inodes) into 2008.1, possibly also vice versa.
The boot-sector that is written by Mandriva 2008.1 can handle both sizes of inodes: normally there should be no problem when using the 2008.1 bootloader to boot into pre-2008.1 system partitions. But the bootloaders of these earlier systems cannot deal with 256-byte nodes. Booting into 2008.1 will therefore fail if the boot-sector has been written by most pre-2008.1 systems. Currenly this is the case for Mandriva 2008.0 and older releases, and also for most other Linux distributions.
Normally the user does not need to explicitely specify what bootloader is to be installed, he accepts the bootloader that is written by default - for instance when a system is installed or when an updated kernel is put in place. During the transition period while partitions with 128-byte and with 256-byte inodes coexist, management of multi-partition systems may require some precautions. The present note explains some items that have resulted from recent forum discussions.
If this sounds too complicated, well : imagine you are using Word 5. Word 6 appears and you cannot read anymore these new Word 6 files. Users of Word 6 can read both Word 6 and Word 5. We played this game before, but now it's free...