Possible bug in accessing methods documentation?

Hi,

Reading help("Documentation"), I'm led to believe that a help call
like:

    ?myFun(x, sqrt(wt))

Will search for help on the appropriate method in the case that myFun
is generic.  This isn't working for me.  Here is an example using the
Biobase package:

## If Biobase is not installed
source("http://bioconductor.org/biocLite.R")
biocLite("Biobase")

library("Biobase")
data(sample.ExpressionSet)
class(sample.ExpressionSet)

[1] "ExpressionSet"
attr(,"package")
[1] "Biobase"

z <- featureNames(sample.ExpressionSet)
z[1:2]

[1] "AFFX-MurIL2_at"  "AFFX-MurIL10_at"

?featureNames(sample.ExpressionSet)

Warning message:
no method defined for function 'featureNames' and signature 'object = "missing"' in: .helpForCall(e1Expr, parent.frame()) 
Error in .helpForCall(e1Expr, parent.frame()) : 
        no documentation for function 'featureNames' and signature 'object = "missing"'


Am I expecting the wrong thing or is this broken?  

+ seth