get posts by custom field after update_post_meta

i have following problem: i create a few hundred posts based on a CSV file. each posts comes with some custom attributes which i create by using

update_post_meta()

so far everything works fine, but as soon as i try to select these posts via get_posts() i don’t recieve the items unless i open the items in the backend, save them (without making any changes). Since the import will run on a daily basis, re-opening and re-saving each and every post is not an acceptable solution.

anyone any hints? thanks in advance

Stefan