Prusa Slicer with Ender 3 Pro Direct Drive  

RE: Prusa Slicer with Ender 3 Pro Direct Drive

Try actually checking in the printer profiles.  I have an ender 3 profile installed not the pro but in that profile the printer is set for a 2 stage warmup.  So the thing you describe as a bug, isnt.  Its doing exactly what its supposed to.  The Printer Settings>Custom Gcode>Start Gcode contains the following -
G90 ; use absolute coordinates
M83 ; extruder relative mode
M140 S{first_layer_bed_temperature[0]} ; set final bed temp
M104 S150 ; set temporary nozzle temp to prevent oozing during homing
G4 S10 ; allow partial nozzle warmup
G28 ; home all axis
G1 Z50 F240G1 X2 Y10 F3000
M104 S{first_layer_temperature[0]} ; set final nozzle temp
M190 S{first_layer_bed_temperature[0]} ; wait for bed temp to stabilize
M109 S{first_layer_temperature[0]} ; wait for nozzle temp to stabilize
G1 Z0.28 F240G92 E0G1 Y140 E10 F1500 ; prime the nozzle
G1 X2.3 F5000G92 E0G1 Y10 E10 F1200 ; prime the nozzle
G92 E0

Notice the M105 S150 in there.  You describe it going to 150 degrees, that line is telling it to do so.  If you leave it going you will see that the extruder will heat up to print temps before it starts using the M109 S{first_layer_temperature[0]} ; wait for nozzle temp to stabilize line.

I dont know about your extruder 'tow' back problem as Im not sure what you mean by that.  Given the Ender 3 basic is a bowden printer and you describe having a direct drive I suspect you need to set a proper retraction value for your printer.  Bowden printers require massive retraction settings compared to direct drive.  For example I  had a CR10 that had 6mm retraction set in the default profiles.  When I modified it to direct drive I needed to set it to 0.8mm which is far more reasonable for a direct drive printer.  The Ender 3 profile has 5mm retraction set.  Given you are getting 10mm which is double then I'd suggest check not only your prusa profile but also octoprint.  Octoprint can and does change settings received from slicers when configured to do so.  So if octoprint is set to handle retraction and has 5mm in there but the slicer is also doing its own retraction then its quite possible to have 10mm.  Thats why direct printing without octoprint is always a good idea to start with as you are removing another source of potential errors.  Once you have slicer>printer working and configured correctly you then add in octoprint.

Trying to print with a profile designed for a different printer is almost certain to cause issues.  Try to find someone who has your printer and ask them if they have a suitable profile for the slicer you intend to use.  

RE: Prusa Slicer with Ender 3 Pro Direct Drive

Thank you for your helpfull reply. I will try to print directly from the sd card and bypassing octoprint. I could really be that octoprint might do some mess here. The problem with the tow back or retracting is that it moves the filament by 100 mm not 10 mm. This causes the filament to completely move out of the extruder and stop extruding filament. Lets see if this might help solve the problems.

RE: Prusa Slicer with Ender 3 Pro Direct Drive

I found the problem within Octoprint, at least part of it. I disbled the Octolapse plugin and the problem with the long retraction was gone. I think it simply has to do something with the settings inside the octolapse plugin. 
I also figured out that in the start code, the temperature was set to reach 150 degrees until the hotend had done all the movements (homing, autolevelling etc) and then started to go to the right temperature. This was in order to prevent filament running out of the nozzle !

Thanks for your help !