Bing is following the leader on close variants. No longer will true exact match exist in Bing Ads. On May 21st, Bing Ads will be making two changes to the way keywords are handled.
The Addition of Close Variants
Close variations include misspellings, singular and plural forms, acronyms, stemmings (such as floor and flooring), abbreviations, and accents. The problem is sometimes the plural keyword performs differently than the singular keywords. Or a stemming means something different (ie. printer & printing).
Deprioritization of Negative Terms
This is a tricky one. No longer will single negative keywords stop phrase keywords from showing. For example, usually you could add "free" to stop "free shoes." Starting May 21st this will not work anymore. Now you must use the [free shoes] negative match. Plus, if you have [free shoes] positive and [free shoes] negative, Bing will prioritize the positive over the negative.
The good news is Bing gets more money from advertising but it creates a headache for advertisers.