After having a few months of problems using PHP and fopen('zip://something.xlsx#xl/worksheets/sheet1.xml', 'r'), I finally found the reason of that exact line of code giving errors on some PC's... Assuming this uses a call to parse_url under the hood, I tried parsing this, resulting in the following URL parts:
[scheme] => zip
[host] => something.xlsx#xl
[path] => /worksheets/sheet1.xml
That's just not correct... Parsing should return the following:
Conclusion: beware when using parse_url and the zip file wrapper!