Hi,
From what you wrote before, I understand that you're using the "table" layout for your products listing.
However, the table layout doesn't display the description of the product at all by default.
If you switch to "div" with the "image and description" item layout, you should see that the description of the product displays up to the read more tag, like for the description of the category.
What all of this means is that I think you (or someone on your end or your template provider) must have customized the product / listing_table view file in order to add the display of the description, but instead basing himself on the code in product / listing_img_description in order to have the description cut at the read more tag, you used some other code.
So you'll have to edit the product / listing_table view file via the menu Display>Views in order to look at the code and correct the code for the description display based on what we have by the product / listing_img_description view file.