After MediaWiki.org was updated to MW 1.19 I noticed my global scripts were not being loaded sometimes.
I replaced the content of [[mw:Project:Sandbox]] by the code
window.console.log( 'ok' );
to [[mw:Special:MyPage/common.js]]. When I opened [[mw:Special:Random]] a few times, I was expecting to always get the "ok" message in the error console, but this only happened some times. When it didn't, a SHIFT+Reload solved the problem for that page, but then if a opened another random page the problem is back again.
I've reproduced this on Google Chrome 17.0.963.56 and Firefox 10.0.2.