directory size inconsistent between "du *" and "du file"

Question

Can someone help me understanding this ?

# du -hs *
3,8M    depmodwrapper-cross
712M    linux-karo
211M    u-boot-karo

# du --apparent-size -hs *
3,6M    depmodwrapper-cross
672M    linux-karo
176M    u-boot-karo

# du -hs u-boot-karo
584M    u-boot-karo

# du --apparent-size -hs u-boot-karo/
524M    u-boot-karo/

There are more info about filesystem and number of files

# df -h .
/dev/md3        822G  658G  123G  85% /mnt/tmp

# mount |grep /mnt/tmp
/dev/md3 on /mnt/tmp type ext4 (rw,relatime,data=ordered)

# find u-boot-karo/ |wc -l
28392

Forced e2fsck do not fix this. What does this mean ?