[R] lme4 question

[Lawrence Hanser]

Dear R Colleagues,

I run the following two models:

mod1 <- lmer(y ~ category + subcomp + (1 | id))
mod2 <- lmer(y ~ category + subcomp + category*subcomp + (1 | id)

where:
category has 4 possible values
subcomp has 24 possible values
id has approx 120 values (id is nested within category, and in unequal
numbers--i.e., unbalanced)

Then to look for differences in the models I run:

anova(mod1, mod2)

I receive this warning message after the last command:

In data != data[[1]] :
  longer object length is not a multiple of shorter object length


I think I know why this is happening (i.e., the two models are of
different length).  Is my surmise correct?  If I am correct I don't
think I should worry.  Should I?

Thanks.