[Q] Yahoo Email - IMAP not deleting Emails topic

On my wifes S5, we set up yahoo with the stock email app as IMAP.
Whenever she deletes an email it reappears, usually minutes, after deleting it.
I have heard this is a known issue. She is on Kitkat.

Does Lollipop fix this issue?

I have an S5 also, i set my yahoo up as IMAP with the stock email app.
I have no issues deleting my emails. We both have verizon S5's.

Any thoughts or suggestions?
Thank you for your help in advance.

[Q] Deleting Cached Data topic

Hi, I have a friend who decide to get this phone against my personal suggestion, now the issue is I that have no clue how to delete the cached data, I own Galaxy phones and Nexus, that I know where to go to delete the cached data, however I can't seem to find that option on HTC, nor if I boot on recovery I'll see this feature.

So the question is, How do I delete Cached Data on HTC?