ROracle: basic insert fails

Hi all,
I've been playing with ROracle (0.5-9) for a few days
and I can't wrap my mind around this one.
Here's a sample of my R (2.4.0) session.

my.df<-data.frame(prd_id=c(123,456),vol_factor=c(.123,.456))

my.df

prd_id vol_factor
1    123      0.123
2    456      0.456

library(ROracle)

Loading required package: DBI

conn<-dbConnect("Oracle","***/***@***")
dbGetQuery(conn,"create table mytable (prd_id number, vol_factor

number)")

dbGetQuery(conn,"insert into mytable (prd_id,vol_factor)

values(123,.123)")

dbGetQuery(conn,"insert into mytable (prd_id,vol_factor)

values(456,.456)")

dbGetQuery(conn,"select * from mytable")

PRD_ID VOL_FACTOR
0    123      0.123
1    456      0.456

the above works as expected. Now let's try to insert new rows into
mytable
using a prepared statement and bind variables:

ps<-dbPrepareStatement(conn,"insert into mytable (prd_id,vol_factor)

values (:1,:2)",bind=c(rep("numeric",2)))

res<-dbExecStatement(ps,my.df)
dbCommit(conn)

[1] TRUE

dbGetQuery(conn,"select * from jdomenge_test")

PRD_ID VOL_FACTOR
0    123      0.123
1    456      0.456
2    123         NA
3    456         NA

so the 2 new rows were appended, except the values in the second
column were seemingly not read...
the same happens with dbWriteTable:

dbWriteTable(conn,"mytable",df,append=T,row.names=F)

[1] TRUE

dbGetQuery(conn,"select * from mytable")

PRD_ID VOL_FACTOR
0    123      0.123
1    456      0.456
2    123         NA
3    456         NA
4    123         NA
5    456         NA

It seems the only way I can insert rows in a table is to build a query
string
and pass it into dbGetQuery.
Note that SELECT queries pose no problem, only INSERT.

I'm clueless at this point, I don't know what I'm doing wrong.
I could find no answer in the help files nor on the web...


Any help would be *greatly* appreciated.

Thanks in advance,

Jean-Christophe