We keep running into an issue on a daily basis. Right now our workflow when entering a ticket is as follows:

1. Open new ticket
2. Enter subject (1st copy-paste) needed to copy subject to description as similar words used. We add addl info after the paste.
3. Tech updates the diagnosis or what they did to resolve the issue.

--------- Entering Invoice ----------------
Usually for business clients we use 'add charges to ticket' as they might have several invoices for monthly billing.

1. click 'add charges to ticket' or create Invoices (to generate single invoice)
2. Either 'remember' what initial issue was but usually go back to ticket and (2nd copy-paste) the initial problem on a line item as customers like to see what they are being billed for.
3. Go back to ticket again and (3rd copy-paste) the diagnosis of what we did to resolve the issue. When the cust receives the invoice all the info is there so they rarely if ever, ask what charges were for.

It works great, but the back and forth to copy and paste gets monotonous to do each and every time. I don't know a perfect solution for this but a small 'copy to clipboard' tiny note or button next to each field would work very well I would think. Or a copy from 'issue', 'diagnosis' etc would work as well. It just feels like there should be a much easier way compared to going back and forth between ticket and invoice to enter things.
An mock up sheet of one we just ran into today for example can be seen here: https://dl.dropboxusercontent.com/u/13180231/RShopperExample1.pdf