Not too confident in my terminology but :sprinting a string that has been evaluated down to its spine seems to fully evaluate the string:

Prelude> let a = map (Debug.Trace.trace "!!!") "abc"
Prelude> a `seq` ()
()
Prelude> :sprint a
a = _ : _                     -- looks fine
Prelude> length a
3
Prelude> :sprint a
a = "!!!                      -- strange!
a!!!
b!!!
c"

What I expect to see is a = [_,_,_]. :print behaves similarly. Since neither :print nor :sprint is supposed to force any evaluation this seems like a bug. At least it can make debugging quite confusing if you're not aware of it!