It is pointed out that an example due to J. Pachl shows the nonexistence of regular conditional probabilities in Doob's sense when the underlying space is a perfect probability space. This answers a question of Sazonov.
"A Note on Regular Conditional Probabilities in Doob's Sense." Ann. Probab. 9 (5) 907 - 908, October, 1981. https://doi.org/10.1214/aop/1176994321