Testing R75753 on VirtualBox 5.1.26 :
If I try to install ReactOS to a partition, which 450-512 MB size, usetup partitions it as a FAT16, formats and does the first stage to the end without hickup.
After reboot, if the instalation CD is not removed, there is the text displayed on the screen asking to press any key to boot from CD....
If I choose not to press any key, it procedes to boot from the hard drive and hangs. There may be two variants:
it hangs with a frozen cursor a line below the text or
clears the screen and hangs with the frozen cursor in the top left corner of the screen.
If the partition size is 513+ MB, usetup creates and formats the FAT32 partition and the 2nd stage procedes as expected.
The bug is exposed from 0.4.1 (Looking only to the releases of 0.4.x series), as 0.4.0 demanded for at least 550 MB partition to install and the requirement was changed to at least 450 MB.