This problem is when the altitude has a decimal value.
It happens when you try to edit the station as well with a non-integer altitude value. I think the following diagram from the overview shows where the potential error might be. Adding input validation and feedback might be a good step in resolving this issue properly.
In network/base/models.py line 46, the following is resulting in the request message yielding an error:
alt = models.PositiveIntegerField(help_text=‘In meters above ground’)