One of our coders have pinged me that he is getting a weird error message "Warning: uksort(): Array was modified by the user comparison function". The array sort callback was doing a database query on the first run, stored the results and used that to sort. For sure it was not modifying the parent array. Fairly innocent, isn't it? Well, actually not. It turns out that last August a check was added to PHP 5.2 and 5.3 (released in 5.2.11 and 5.3.1) to verify that the array being sorted does not change, however debug_backtrace() fools this check. Guess what? We use debug_backtrace() when logging queries (like, you know, when doing development) to find the caller of the query. It's also used in watchdog. There is an open PHP bug report for this but I thought a blog post warning people to keep their array sort callbacks simple in Drupal 7 is a good idea.

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