Ok, I figured it out:
There is a gene in your robot:
cond
*.fixpos 0 >
and
*.nrg 250 >
and
*.slime 250 <
start
50 .mkslime store
stop
You may be aware that making slime produces waste.
What is happenin' is your robot is constantly producing more slime, as it is constantly getting more energy from chloroplasts ( .nrg > 250 )
This does not happen in 2.45 due to the fact that a robot is not getting any new energy, that is: .nrg < 250