I was getting this problem too. Sometimes I would temporarily use a 26Gb ramdisk on my 32Gb system. When I was done my special processing task, I would try to unmount and resize the disk back to the its original smaller size. This would always fail and the 26Gb of memory would never get freed. I'd have to reboot to setup up a new smaller size for the ramdisk.
This appears to have been some sort of bug in the Windows 10 memory manager and not with the RamDisk software. After installing the Aug 31 cumulative update to the 1607 version of Windows 10, my problems are solved. I can now resize my ramdisk from 26Gb back down to its normal 3Gb without rebooting now.
And just want to thank the Ramdisk developers. This is a wonderful tool.