When i enter the "if" keyword, intellisense pop up like this
when i enter an open parantesis at this point, R# completes the text with "IFormatProvider"
Completion filters are enabled with the default settings (show filters bar, persist filters, filter state "include" for all contexts except templates)
I'm not sure if it's a bug. I can remember that i had the same problem with an older release (i think at the time the feature was introduced and it occured in some EAP builds). If i disable the "Persist" checkbox intellisense works as expected