Mail app not automatically deleting trash emails

iTunes 11.1.2.32 Windows 7 32 Bit

iPhone 4S (and iPhone 4)

iOS 7.0.3

I have my own domain name for my email.

I can access via POP3 SSL and IMAP SSL

My first iPhone was a 4 which i used July 2010 to July 2012. I July 2012 i upgraded to my current 4S.

I use Windows Mail on my PC to access my email via POP3 SSL as i have no need to keep messages on a server any longer than i need to.

I use the Mail app on my iPhone to access the messages via IMAP SSL. Up until iOS 7 i would check my emails using the iPhone and delete any messages to the Trash folder On My iPhone (not on the server). I would have it set to delete the deleted messages After One Day so i had a 24 hour safety buffer.

This way i could use the iPhone as a quick check on my email and also use it as a Spam filter. If i needed to reply to an email from my iPhone I would and cc myself in if i needed a copy. One or twice a week i would fire up the PC and download the messages in the Inbox to the PC in Windows Mail.

This arrangement worked flawlessly for 3 years until i updated to iOS 7. Now the deleted messages in my Trash folder stay there until i manually remove them. I've tried:
-deleting and resetting up the account again in the iPhone
-changing the setting to One Month, saving the change and then setting it back to One Day and saving the setting.

-checked with my domain/email provider that i'm using the correct settings.

-changed IMAP Path Prefix from \ to INBOX, which works the first time but then fails to work again (i.e. each time i change it to \ and then back to INBOX it clears everything over a day old at that point but then doesn't do it again)

My wife has my old iPhone 4 without a SIM and uses it as an email checker for her account as well as for surfing the net and Facebook etc. She has the same setup as me (but seperate email account on my Domain) it all worked fine on that too until the update to iOS 7.

Is there a setting that might have gone out of line here or something i've missed?