S4 summary method not being called (VGAM)

The symptom triggering this email is that an S4 summary method sometimes refuses to be invoked, even when a package is explicitly loaded, if the first load of the package is implicit. It may or may not be specific to 'summary' methods and/or the 'VGAM' package. I've sent to R-devel because (i) it looks like some kind of bug to me, but I'm not sure; (ii) it's not something I personally need any help with; and (iii) it seems a bit specialized for R-help.

Here's the case notes. I have an object 'nf1' of S4 class 'vglm', created by calling 'vglm(...)' from package 'VGAM' (you can create your own from the examples in VGAM). It's save()d into a file "nf1.rda". If I start a new R session, call 'library( VGAM)', and then 'load("nf1.rda")', then 'summary(nf1)' works fine. But if instead I start a pretty basic R session and load() the file *without* having explicitly called library( VGAM), the summary method for 'vglm' doesn't get called whether or not I subsequently call library( VGAM). Transcript below.

I'm using R 2.13.2 on Windows XP, VGAM 0.8-4. The same thing happens with R 2.15 devel v57866.

bye
Mark

Mark Bravington
CSIRO CMIS
Marine Lab
Hobart
Australia


#############################
# Start a basic R session, and then:

  search()

  [1] ".GlobalEnv"        "package:stats4"    "package:splines"   "package:stats"     "package:graphics"
  [6] "package:grDevices" "package:utils"     "package:datasets"  "package:methods"   "Autoloads"         "package:base"

print( load( "nf1.rda")) # which should implicitly load VGAM, but not attach it

[1] "nf1"

search()

# ...snipped. No explicit VGAM

loadedNamespaces()

# ...snipped. VGAM is there at the end.

nf1

Call:
vglm(formula = form, family = posbinomial, data = data, trace = TRUE)

Coefficients:
# ...snipped. The print() or show() or whatever method seems to get called OK

summary( nf1)

Length  Class   Mode
      1   vglm     S4

# Hmmm... default method is being called, that's wrong. Try explicitly attaching 'VGAM':

library( VGAM)

Loading required package: splines
Loading required package: stats4

Attaching package: 'VGAM'

The following object(s) are masked from 'package:splines':

     bs, ns

The following object(s) are masked from 'package:stats':

     biplot, case.names, coefficients, df.residual, fitted, fitted.values, formula, poly, residuals,
     variable.names, weights

The following object(s) are masked from 'package:base':

     identity, print, scale.default

summary( nf1)

Length  Class   Mode
      1   vglm     S4
# Hmmm... even though VGAM is on the search path etc, the wrong method is being called

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