PocketMine is having this problem running PHP 7 on Windows, according to my tests on W8. https://twitter.com/PEMapModder/status/676065841000144896
Same problem on Linux, actually Using pthreads 3.1.5, it has this issue, fixed in (but not sure if there aren't other issues): https://github.com/PocketMine/PocketMine-MP/pull/3802 Using binaries compiled with: Spoiler: a fork of shoghicp's script