I have to be upfront and tell you that I have no experience on the RK tractors, however I do have experience on hydrostatic transmissions. So I will try and work through some traditional troubleshooting techniques.
So here we go...
Is this something that just started happening or has it been gradually getting worse over time?
Could you provide any picture of how the pedals are attached to the hydrostatic transmission? I need to figure out if this is a transmission that has its own neutral or if it relies on the tractor linkage to adjust neutral.
Does the literature mention who the transmission manufacturer is or any model number?
Let's start with this, I am sure there will be some more questions.