I'm a littile bit
with this problem.
I have configured Instapaper to send the pending read news to my Kindle Touch in a diary base. I receive and read them well, but I cannot delete them.
Does not matter what amount of time I put my finger in the file, ti do not opens the properties window that allows to delete it.
It only happens with Instapaper stuff.
Of course, connecting via USB files can be deleted.