I did a split to set up 2 vertical tab groups. (see first screenshot). I closed and reopened SE. The tabs for both groups still appear, but the window for the second group seems to have disappeared (see second screenshot). I have to do right-click/New Vertical Tab Group on the second tab to get it back the way it was.
SlickEdit 2013 (v18.0.0.5 32-bit)
Serial number: FE25543_BETA
License type: Beta License
License expiration: 2013-07-24 12:01:00
License file: C:\ProgramData\slickedit\18\slickedit.lic
Build Date: April 23, 2013
Emulation: CUA
OS: Windows 7
OS Version: 6.01.7601 Service Pack 1
Memory: 73% Load, 2452MB/3318MB Physical, 3151MB/6635MB Page File, 231MB/2047MB Virtual
Shell Info: C:\Windows\system32\cmd.exe /q
Screen Size: 1920 x 1200
Project Type: Cpp
Language: .h (C/C++)
Installation Directory: C:\Program Files\SlickEditV18.0.0 Beta1\ (non-removable drive,NTFS,221927MB free)
Configuration Directory: U:\MyDocs\My SlickEdit Config\18.0.0\ (remote,NTFS,31651MB free)
Spill File: C:\Users\david.hohl\AppData\Local\Temp\$slk.5 (non-removable drive,NTFS,221927MB free)