We've recently got an interoperability bug report for Microsoft Edge that was rooted in "word-break: break-word". Chrome in this case breaks as if overflow-wrap/word-wrap is set to break-word and Edge/Firefox don't. Looking at the latest draft for CSS Text (http://dev.w3.org/csswg/css-text/#word-break-property) I see the expected values for word-break don't include break-word, which lives as a property under overflow-wrap/word-wrap. Looking at the usage data word-break: break-word is used on 3000 sites from the set of 1 000 000 unique sites. Brief analysis suggests this might be mostly coming from couple JS libraries - but it doesn't look like any of them depend on it. 1200 hits out of 3000 are for the single library, which we'll outreach to following this bug as well. I'm Program Manager in Microsoft Edge/Internet Explorer Layout team and filed this bug after discussing with internal developers and CSS WG (http://lists.w3.org/Archives/Public/www-style/2015May/0259.html)
Also filed Chromium bug - https://code.google.com/p/chromium/issues/detail?id=492202 (I suspect this property: value is coming from WebKit, but might be wrong)
It sounds like the relevant Working Group has standardize the current behaviour,