My dmg file not asking for password anymore

If "Remember password in my keychain" was inadvertently selected as displayed below,

...search for a file in Keychain Access>login>Passwords>/<foldername>.dmg

I created an EDI, named "Untitled," checked the "Remember" option, and this is what appeared in the search field when I entered .dmg

Deleting that password, reenabled the requirement for the original password to open the Disk Image.

stgnzz wrote:

It must have been some other glitch.

In that case, just create a new EDI, and move your files to that Disk Image which will restore your password protection.