Using front left eye without turn knob left back eye will come on?

Almost certainly the switch, not the element, Had the same problem on a different stove - went to 10 no matter what the knob was set to.
Here is a parts list, you should be able to get the part from a local appliance part seller. I used ReliableParts in my town.

https://www.partselect.com/ModelSections.aspx?ModelID=815598&ModelNum=KECD805HBL3&mfgModelNum=&ManufactureID=3&Selected=ZPGZLZRB&Position=2&mfg=Whirlpool&Type=Cooktop&Mark=2

Control behind knob needs replacing.

SOUNDS LIKE THEY ARE HOOKED UP WRONG CHECK THE HARNESS SWITCH CONNECTIONS OR YOU MAY HAVE A BAD INFINITE SWITCH

so sorry for the way late reply!
if the knob does not fit you'll need a new one...
i found them here....
https://www.repairclinic.com/Shop-For-Parts/c31-x72636333303234/Rcc3024-Knob-Dial-Button-Parts
not sure which is yours as the model # should have a few more # or letters. Take a look at them and see if one matches.
best to you.

you have a bad set of switches and or a spark mod..

You may already be aware of this but ... If our ilve ceran cooktop is the same as yours turn the knob past the 12 setting till you feel pressure and it springs back. This is the switch to fire up the marked outer elements.

http://www.goedekers.com/assets/PDF/FiveStar/ttn6257-manual.pdf
How to Replace Knobs on Gas Stove Gas Stoves Ovens

How to Fix Knob on Gas Stove DIY Removing Stuck Knob Without breaking switch shaft

The igniters for the burners are all on one circuit so when you turn the burner to light the switch inside the burner valve will cause all burner igniters to come on. As far as the left burner not sparking it could be due to a bad igniter switch in the valve and when you turn on the right burner you are causing all(including the left one) to spark. You will need to make sure that the burner eyes are clear and not plugged. You can use a sewing needle to clear out the eyes. The small eyes at the igniter electrodes are very important because if they are clogged the burner will not light.

It sounds like the round burner orifices are dirty. Remove the round orifices and clean in warm soapy water, using a plastic scrubber or toothbrush to remove and dirt and residue around the sides of the burner. Do the same on the little electrode that protrudes at some position around the burner orifice seat.

The system works by the spark ignition module knowing a gas knob is open, and sensing for a flame by ionization within the exhaust gases of the flame. If things are dirty, then the module cannot read the ionization and shuts down the burner, and will also cause the spark to continue.

Also make sure all the burner orifices are properly seated in their holder. If not, the same thing will happen.

probably a worn wire to the electrode or a cracked ignitor. you are faced with taking off the hobtop and looking - no easy solution. you should not do this unless you are confident and don't interupt the gas path