Slic3r retraction strange behavior

When I enable the retraction of slic3r ， the extruder always lost steps during retraction， but forward are correct。
after check Gcode， I found code like this

G1 X-27.837 Y5.703 F3840.000 E14.84644
G1 X-28.497 Y4.623 F3840.000 E14.47068
G1 X-28.927 Y3.443 F3840.000 E14.09783
G1 X-29.166 Y2.453 F3840.000 E13.79541
G1 X-29.571 Y0.182 F3840.000 E13.11032
G1 F1200.000 E13.01032

My retraction setting is 20mm/s and 2mm, but those code seems run the retraction at 64mm/s ( F3840) , My extruder
can't run at that high speed. i wondering how such a high speed came from? My travel speed is set at 80mm/s, not 64mm/s
either. Any suggestion?

I've seen this sort of issue before with Slic3r.

If you're running Marlin or Sprinter, you can limit the max speed of the extruder there. This doesn't solve the Gcode, but it does at least solve the issue.

Find the reason,

It caused by the "Wipe while retracting" settings, Just uncheck that checkbox and everything are OK.

So it should be a "bug" of the implementation?