The extension Array#to_hash in this gem breaks Kernel.exec when called with these params:

[cmdname, argv0], arg1, ... : command name, argv[0] and zero or more arguments (no shell)

Observed on ruby 1.9.3-p448 and 2.0.0-p247. The nature of the failure is an ENOENT exception where it appears that exec attempted to execute the first argument rather than the executable. Demonstration gist.

This form of Kernel.exec is used by childprocess which is used by selenium-webdriver, so this interference prevents an application which uses this gem from being tested with selenium-webdriver (via capybara or otherwise).