Please read here what IDM wrote why this function MUST be removed by IDM Computer Solutions, Inc. It is not a bug, it is not an unintentional broken code, it was an intentional removal because of a software patent another company has. Open source and freeware applications violating this software patent can still offer a split workspace feature simply because the company owning the software patent can't sue a company for damages. But IDM Computer Solutions, Inc. is a company which sells licenses for UltraEdit and can be sued therefore for damages. Yes, in US there are companies with the business model finding a US Patent Office which applies a patent for a GUI feature and then sue other companies for damages, damages this company never really had.
Best regards from an UC/UE/UES for Windows user from Austria