Newly installed version; can't run lm function

New installation seems to have behavior I cannot figure out.  Here is illustrative sequence where I load a small data set (test) from Crawley's files and try to run a simple linear model and get an error message.  Oddly, R reports that the variable 'test$ozone' is numeric while, after attaching test, the variable ozone is not numeric.  Can someone please help?  This behavior is occurring with multiple data sets loaded from outside R.  Thank you in advance.
Michael Grant


Example:

test

    ozone garden
1      3      A
2      5      B
3      4      A
4      5      B
5      4      A
6      6      B
7      3      A
8      7      B
9      2      A
10     4      B
11     3      A
12     4      B
13     1      A
14     3      B
15     3      A
16     5      B
17     5      A
18     6      B
19     2      A
20     5      B

is.data.frame(test)

[1] TRUE

is.numeric(test$ozone)

[1] TRUE

is.factor(test$garden)

[1] TRUE

lm(ozone~garden)

Error in model.frame.default(formula = ozone ~ garden, drop.unused.levels = TRUE) :
   invalid type (list) for variable 'ozone'

attach(test)
is.numeric(ozone)

[1] FALSE

is.numeric(test$ozone)

[1] TRUE

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