Beware of evil pathauto patterns!

Recently, a very mysterious problem has cost us quite a lot of time and some headache too. Before I explain, what happened, I want to mention, that it happened on a Drupal 7 Site on a MS SQL Server database. According to an issue on, that I will mention later, it may also occur with PostegreSQL, but most likely not with MySQL. But I also have a general advice regarding pathauto patterns and best practices.

Fatal errors may cause infinite Feeds batch runs and exasperate you!

Every developer knows that kind of situations, where you spend hours chasing a problem, that suddenly appeared, and the more you debug and dive into fixing it, the more you get confused and unnerved. And when you finally have found the solution, it turns out, that it was a very simple and stupid bug, you've created unwittingly - the sort of cause, you haven't ever thought about, and you feel like bumping your head hard onto the wall...