When you right click on a drive letter in explorer you should have the option to "Unmount Imdisk Virtual Disk".
"Eject" is a function of the OS that is present normally for any "removable" drive.
If you try to "Unmount Imdisk Virtual Disk" on a non IMdisk drive letter you should have a message "Not a IMDISK Virtual Disk : <drive letter>".
This (and possibly the other "bug" you experienced) is probably related to the "peculiarities" of IMDISK (by design).
You have to understand how the name is completely inaccurate.
IMDISK does NOT provide a "disk" (the disk is the "whole thing", i.e. a \\.\PhysicalDriven in Windows) but rather a volume or "drive" (i.e. the *whatever* gets a drive letter in Windows NT).
As an example any IMDISK device is not seen in Disk Manager or in Diskpart, and not even in Mountvol (so it is not really-really even a volume) simply the virtual *whatever* it creates is not a "full disk device" (like as an example Arsenal Image Mounter is) and it is hooked to the running OS at a "higher" level than a "real" disk device.
A number of programs, API calls, etc. may have been targeted to "real" (or "virtual") disk devices, and they will throw a fit when accessing IMDISK virtual drive.