[Dovecot] file->buffer_offset + file->buffer->used == file->sync_offset

I got the following panic on 1.2.3:

Panic: file mail-transaction-log-append.c: line 88 (log_buffer_move_to_memory): assertion failed: (file->buffer_offset + file->buffer->used == file->sync_offset)

It's probably related to the file system holding the indexes being full.