Completely ignoring a user is difficult. You mentioned noticing the user in quotes by other users. There is also forum search functionality and topic listings to consider.
By only seeing the selected quotes of a user, it is very easy to get a (more) skewed view of how that user behaves. A long, insightful, post can have selected phrases quoted by another user that completely distort the meaning of the post. You only see these quotes and get the opinion that the user is still wrong/incorrect/ignorant and pat yourself on the back for ignoring this user's contributions. In reality, you've missed a vital part of the conversation and by not providing a way to see the entire contribution, the admins have made it impossible for you to get this information unless someone else block quotes the user's entire post.
Searching on the forum, unless implemented to ignore users, is likely to return results from the ignored user. If you don't realize that and click on the search result to see more information, you are taken to a post that appears not to exist. You are confused and frustrated at the search results. Alternatively, the search may see the quotes of this user in another user's post. This brings us back to the first point.
Finally, on topic listing pages, what is the expected behavior when an ignored user posts a new topic? Does the entire topic not get shown? In that case, you miss out on an entire conversation. Does it show the topic listing with no content? This is next to useless as you now know the user said something, but you don't know what. You also have no way of knowing what was said until the post is quoted by others.
There is another reason, I suspect, for this partial ignore. What happens if you ignore an admin? Does the software allow this? If it does and an admin makes an announcement topic, how are you to know what is going on?
The point of the "partial" ignore is to let you know that something was said. It gives you the option of seeing what that is, but it does not present the entire post to you without the additional step of deciding you want to see it. It allows you to remain in the loop by seeing all contributions.
You actively chose to ignore that user. Later you see a quoted post and one way or another want to respond. It is incumbent on you to know the entire context of the quote so that you can provide a good response. You took the step of reducing conflict by ignoring them. That good behavior should spill over when you chose to interact with this user. Be the bigger person and read the post and reply to relevant portions.
If the post turned out to be similar to others and the cause for you ignoring them in the first place, continue to do so. Just because you can now see the post doesn't mean you have to reply.