I have:
SlickEdit Pro 2015 (v20.0.0.12 64-bit)
Build Date: November 03, 2015
Emulation: Vim
OS: Linux
OS Version: Fedora release 20 (Heisenbug)
Kernel Level: 4.0.4-101.fc20.x86_64
Build Version: #1 SMP Wed May 27 21:12:19 UTC 2015
Processor Architecture: x86_64
X Server Vendor: The Cygwin/X Project
Memory: 90% Load, 1043MB/1149MB Virtual
Shell Information: /home/bjkurlex/slickedit/bin/secsh -i
Screen Size: 1920 x 1200, 1680 x 1050, 1600 x 900
Project Type: Gnuc
Language: .command (Plain Text)
Encoding: Automatic
I blew away my .slickedit directory and tested on a clean installation.
Create a clean workspace/project (I created a gcc c project) with a Makefile and a C file (foo.c with simple "hello world" app).
Load both files in the project so that they are in the buffers list. For this example, I had foo.c as my actively viewed buffer.
Enter via vim command mode
:b Makefile
A new, odd buffer of .command<0> shows up and is presented. This unexplained buffer can't be removed until you exit the program. (:q, or close or other various means of removing a buffer).
This was encountered by a finger memory attempt. That is, in vim, you can request a file buffer by name via :b <filename> in addition to the use b <buffer number>. I understand this isn't supported (yet), but I wouldn't have expected the odd results when passing a non-numeric value to the colon command.