Directory in my mac filesystem has sub directories with greater size than parent directory

I have some weirdness on my mac's filesystem nowadays.

I have a dir in my home dev to store my programs and git repos. Size of the dev is 630 MB. Size of the dev/todos is 637 MB and there a re some other sub dirs in this dev of 175MB and so.

What is the reason for that. Is my mac going crazy or it is git or something?