I've figured out what's going on. The timeout SlickEdit is using on Windows isn't long enough. SlickEdit is fooled into thinking you want to drag the selected text. For some reason the LButtonUp event is'nt coming in fast enough when you click from the middle part of the touch pad (weird). SlickEdit is using a Windows system call to get the timeout but it just isn't long enough (200ms). For 27.0.2, I'm going to change the code to use 500 milliseconds and not bother making the system call. Qt seems to use this as it's hard wired setting for Windows.
As a workaround, load the attached macro below. When the macro is loaded and when SlickEdit is invoked, it will set SlickEdit's drag delay to 500 milliseconds.
Macro>Load Module...