PolyMC may allow offline accounts, but OLauncher is a legitimate launcher, using old 2013 Java launcher as it's base (also wonder why no one mentioned MultiMC or it's fork, Prism Launcher).
Uh, MultiMC and Prism allow offline accounts, too - unless you're referring to a fork of Prism that calls itself by a misspelling of PolyMC that integrates a cracked skin server also used by a infamous, malicious Russian launcher. It's also not a bug, it's a feature of the game.
(Also, given that, at the very least, Notch's own stance on piracy has always been reasonably lax, I wouldn't be too bothered about it, especially if we're talking versions prior to 1.8.1-pre4, i.e. before the sale to Microshite.)