Chance Garcia has posted about an exception he's come across several times in using the Zend_Log component of the Zend Framework but hasn't been able to figure out - until now (with the help of part of the Zend Framework manual).

There are a few times I’ve gotten this particular exception and then look at the trace and can’t figure out what’s wrong. More often than not, I’ll get to the line in the trace and be like, "wtf! there’s no priority here. It’s a method call not a constant". [...] So to save myself and others some time and aggrevation, I’m going to go into a bit of detail as to why you may be getting this exception.

As it turns out, the Zend_Log exception was caused by the components overloading of the __call function to allow for some custom handling. Chance sees this issues as an example of "flexibility leading to complications that require complex understanding".