Logistic regression threshold

Hello all,

I am doing a simple logistic regression exercise (no SVM, simple and pure logistic regression) and I cannot understand how rapidminer defines the threshold for classifying instances as "yes". In similar posts it was mentioned that it chooses automatically 0.5, but that is not the case. I downloaded all the "yes" predictions and sorted them in ascending order: the threshold is 0.3108. Why?

I am using the "default" instance from the ISLR library (https://cran.r-project.org/web/packages/ISLR/index.html).

Thanks in advance,

Bernardo