When you get printing make sure you calibrate your extruded. I had to chance my steps per mm from 134 to 155 and now everything is perfect.
Yep this is a known issue! I'll be uploading new firmware soon to fix this. I have no idea why the calculated value was wrong or how I missed it for so long but a few days ago I decided to properly calibrate my extruder like you did and I got almost exactly the same steps/mm.
I would also recommend that everyone manually calibrates their extruder in order to ensure the steps/mm is correct before printing!