All I have been doing is selecting the bit I wanted in the previous post, putting the posters name and then pasting the bit I wanted to quote. I didn't realise I was deleting anything.
Ah, well that makes sense then Ody, as it sounds like you're 'manually' creating the reply, rather than allowing the board software to help do it for you, and for the software to do it in a way that activates the relevant notifications and also makes the posts easier to read in terms of allowing readers to see who you are replying to.
Towards the top right of any post you want to reply to, you'll see a 'double-quote' icon - it's to the right of the 'report this post' button. If you press that, the TLF board software will automatically format a reply to the post, allowing you to then type your reply underneath it the original post.
Give it a go using the 'Preview' option instead of actually committing a post, and you'll see it working as expected.
Of course you will often want to remove some parts of the post you are replying to (and it does help a great deal with the readability of replies when people do spend a few seconds doing this.....), but at least the replies are much better to read then, and as I've said, if the person you've replied to has got the auto-notifications turned on, then they are sent a board-notification to say that there is a reply to one of their posts, and the notification then also allows them to jump to the reply itself, if they want to read it straight away, which of course helps the general discussions flow smoothly on the boards, and helps people avoid missing important replies if those notifications aren't activated correctly by your type of 'manual' replies.
Sometimes when editing down a quoted post, it can be fiddly to get to where you want to be, so often I will use the clipboard to hold the section of text that I want to be inside the quote, and then just delete everything inside the 'quote/un-quote' braces, and then simply paste in the smaller section of text that I want to leave in.
When formatting a reply using the above option, I always like to manually insert a blank line after the initial auto-generated 'user-being-quoted' braces, as I think that helps to format the reply a bit better for reading, but that's just a personal choice.
Hope the above helps.