[R] R-squared value for linear regression passing through origin using lm()

[Etienne Toffin]

Hi,
A have small technical question about the calculation of R-squared  
using lm().
In a study case with experimental values, it seems more logical to  
force the regression line to pass through origin with lm(y ~ x +0).  
However, R-squared  values are higher in this case than when I  
compute the linear regression with lm(y ~ x).
It seems to be surprising to me: is this result normal ? Is there any  
problem in the R-squared value calculated in this case ?
Etienne Toffin