And did you follow the steps in the Answers article? Did that fix your problem? (I can't test since I don't have Yahoo mail).

Redirecting

Sign in to Yahoo Mail.
Mouse over the Settings menu icon. Select Settings.
Click Accounts.
Click on your Yahoo account.

Under "Access your Yahoo Mail elsewhere," select POP.
Pick how you want to handle spam emails:
Don't download spam email - No spam is sent to the mail client.
Download spam with no special indicators - Spam is sent to the mail client as-is.
Download spam, but prefix the word "Spam" - Spam is sent to the mail client and says "Spam" in the subject.

Click Save.