I'm 100% convinced that that happened on purpose because it lets Big Mom track their movements without them being aware of it. And since it's a piece of her soul in that thing, she can easily recall it back if they try to use it against her (and probably kill the fuck out of it).
Is it really a part of her own soul? The way I understood it, these homies are created with the souls she sucks out of people, similar to Moria and his zombie army.
During the escape trough the forest, Pudding used her ability to make the souls remember their old lifes to distract them.
Although, Moria was able to call the shadows back when he needed. So im not sure if it was planed (considering Moms condition at the time) but it sure could cause some problems when they face off again.