As per Nightrider
The icing problem on the ground....that was the reason for the after shut down...
Are you sure you are not confusing the use of Engine Anti-ice during taxi in whilst in cold adverse weather conditions? I realize that the Supplementary Procedures contained your FCOM may be different from other operators.
I reviewed the Boeing Factory FCOM and a couple of airlines' FCOMs that I've flown with and there was no mention of leaving the Probe Heat on during the taxi in phase of operation.