Well, we tested and tested, but it looks like a little bug slipped by us in 5.0 that’s probably worth an upgrade. We’ve just released 5.0.1a that contains a fix for it, and we recommend that 5.0 users upgrade. To do that you’ll need to allow upgrading to unstable versions. Here’s a FAQ on how to go about that and upgrade. Not to worry about the stability of 5.0.1a–it contains this bug fix as well as a few other minor ones. It should be completely safe to upgrade. Anyone who installs 5.0 fresh will get the bug fix.
For those interested, the bug fix addresses an issue where line numbers reported in error messages will be offset by two lines. That is, if your script has an error on line 100, the error message will report line 102 instead. The bug fix simply corrects this so that the correct line number of the error is reported.