Why does my LyX convert all images every time it compiles the file?

[Jinghua Zhong]

Hi,

I'm using LyX 1.3.7-3 to edit a file I created using 1.3.5 last year. I 
have both EPS and PDF versions of my figures in the same directory.

With 1.3.5, I seem to remember it doesn't convert my EPS files if PDF 
files are present. (I didn't specify extensions for my figure files and 
I use pdflatex.) However, with 1.3.7-3, LyX converts all my EPS files to 
PDF every time I compile. This makes it significantly slower.

I lost my old 1.3.5 setup during a laptop failure, so I'm hoping someone 
here with more experience can tell me if I'm missing something in my new 
setup.

Thanks,
Jinghua Zhong