We had a lot of odd behavior with both Next and Out. Previously the debugger would interpret the world until it saw that it was no longer on a specific line, or at a specific stack depth. I changed it recently to let the program run normally, and use an internal breakpoint to control step outs. Next's become like a step out temporarily when you descend into a function and need to get back out to the original line, so some bugs with out showed as bugs with Next, too.
Specifically, any time more PHP code was executed as a "side-effect" of a non-fcall instruction, step out would get lost. In these cases the stack trace gives us the offset of the instruction causing the PHP to run, not the instruction that control will return to as is the case with a Fcall. A breakpoint set there would get missed. This changes the step out logic to recognize such cases (via the fact that a nested VM state was pushed to execute the code) and step out more intelligently. We look at the instruction in question, and determine where execution may go, which might be multiple places. I also made a small change to ensure that we don't stop in generated functions when stepping out, which cleans up the iterator experience quite a bit, and sets us up for proper generator stepping, which will come next.
Mike Magruder