A great find!
How about adding a tester for PHP? Should be simple to do. As a plus, add the required separator characters at the start and end of the test string as PHP functions require, such that you pre-scan the test string to find a character that's not in use.
In sampling about 20 different test samples that validate fine under your .net tester, and after adding a suitable start/end delimiters for PHP, rarely do they work unmodified under PHP. I'd say I get maybe about 30% success rate as-is using preg_match.