The option --boot tells the hex utility all the initialized sections are to be laid out as required by the on-chip bootloader.  This bootloader cannot handle any section which is larger than 0xfffe words.  So, when this occurs, the hex utility splits the section up, and starts another bootload-style record for the next part of the split.  When this happens, the hex utility fails to check the alignment requirements of the section to make sure the the starting address of the second record meets that alignment.