I may be wrong but I think you are mistaken. I've just checked what you describe here and read the relevant section in the user manual:
If Bend Markers have been inserted as the result of transient detection, a very short, highlighted range—visible if zoomed in far enough—precedes the Bend Marker. This range represents the entirety of what has been detected as a transient, and it is important when Studio One quantizes audio based on Bend Markers.
The far left of the highlighted range IS the start of the transient, and if you grab the highlighted range with the bend tool, like I did in the following animated screen capture, you see that stretching happens to the left and right of the start of the transient, not to the left and right of the displayed bend marker.
On the animation you can see how the waveform changes red when bent to the right, and you can see clearly that the red color includes the highlighted transient range, to the left of the bend marker.
I must admit the way transient bend markers appear at the end of the transient range rather than at the start (left) can be confusing, so my request to Presonus devs would be to place transient bend markers precisely on the start of the transient range, which I think most people would find more intuitive.