POMO_Reader->substr() call endless loop?

Question

I'm experiencing a somewhat endless loop in the file mo.php

/wp-includes/pomo/mo.php

when loading the site's default text domain.

The PHP error is:

Fatal error: Maximum execution time of 30 seconds exceeded in ...\wp-includes\pomo\streams.php on line 62

I can work around this by disabling the websites translation, but that's not really helpful. I've updated to the latest wordpress version and the latest version of the translation (de_DE).

I'm somehow puzzled as I never had this problem. The last call in my backtrace consumes nearly 30 seconds. The Function call is:

POMO_Reader->substr( $string = '\000\n<h1>Error establishing a database connection</h1>\n<p>This either means that the username and password information in your <code>wp-config.php</code> file is incorrect or we can\'t contact the database server at <code>%s</code>. This could mean your host\'s database server is down.</p>\n<ul>\n\t<li>Are you sure you have the correct username and password?</li>\n\t<li>Are you sure that you have typed the correct hostname?</li>\n\t<li>Are you sure that the database server is running?</li>\n</ul>\n<p>If y...', $start = 71131, $length = 8 )

Does anybody has a thought about that? I'm running on windows and the files served are on a network share. Never had problems with that setup.