Well the title says it all. As you can see in the screenshot here, all those big files have a waaaay smaller size on disk, but when I click HD properties it´s getting full based on the file size and not the actual size on disk, why? Is that a windows bug?
A file on disk takes up a certain integral number of allocation units. If the size of an allocation unit is 4 kB, a file of 4kB byte will take up that whole 4 kB, and so will a file of only 1 byte!. See any of the many online suggestions for disk allocation unit size, such as How to Geek.
In general, there will always be some loss of space, unless file size exactly matches unit allocation size.
