You are right. The configuration setting is not stored in file ue.ini on exit of UltraEdit v18.104.22.168. I will report this issue to IDM support to get it most likely fixed in next released hotfix version.
I found a workaround for this issue. Open with Windows Notepad or any other text editor the file %APPDATA%\IDMComp\UltraEdit\ue.ini while no instance of UltraEdit is running. Search for a line starting with CSS Image Tips=. I expect that there is no line with that string. Go to section [Settings] and insert below the line CSS Image Tips=0 to disable that feature. Save modified ue.ini and exit the text editor. Start UltraEdit and the configuration setting is unchecked and will be unchecked as long as not modified manually again in ue.ini or a new version of UltraEdit is used with a fix for this issue.
Best regards from an UC/UE/UES for Windows user from Austria