In ICU 53, control of date parse leniency was made more granular - instead of just using the leniency attribute of the DateFormat's Calendar, separate setters/getters were provided for several DateFormat-specific parse attributes as well as the Calendar's leniency. However, per discussion, the old DateFormat methods setLenient/getLenient were supposed to work basically as before for compatibility, by setting multiple attributes, or getting the AND of their settings. This works in ICU4J but not in ICU4C, whose setLenient method is currently this:
The setBooleanAttribute calls pass true instead of lenient as they should, and as in ICU4J below:
Since in ICU4C the default setting is lenient for all of these, this means that backward compatibility for setLenient(FALSE) is broken, it will not set strict parsing behavior. This is likely to cause problems for existing clients.