Having two talktalk logins, one for myaccount and another for the community pages doesn't sit right. it feels dumb.
Why not just have a talktalk profile, as part of your account, that is used for posting gubbins on the community forums.
Your personal details are requested by the community profile anyway, and if you're logging a fault, query or complaint you're asked for your landline number so it can be tracked.
That's a lot of redundant steps.
If it's a "security issue", have a profile linked to the myaccount page, then have a handshake between the two portals (account and community) if/when a customer decides they want to spend time on the forums.
Also, just have a drop down menu for the 'idea labels', it'd be less of a faff given that it's a restricted set of options.