Selecting text in an existing text box with the text tool has gotten super sensitive - if you're not in exactly the correct spot it starts a new text box. I've used illustrator over 20 years I'm sure I'm not imagining this increased sensitivity!

I agree, happens all the time, the cursor must be placed inside of em-box to be able to select. And when you have 120% leading by default, you get this tiny strip of 'false trigger' area, you really wouldn’t need to create new area type object. If you increase leading, you would get even more of this space. I wonder if anyone creates new text overlapping the old?

Say I want to select some text. If I click and drag within a text box, Illustrator assumes that I want to create an additional text box. To select the text I want, I need to position my pointer exactly next to the text.
Can the 'selected' area be expanded to within the entire text box?

Hi,

Thanks for submitting this request , Illustrator team really appreciate this.

We had taken your feedback on this.

Regards
Ankit Goyal

PLEASE fix this. I'm going crazy with all the new text boxes I'm creating on accident. This has disrupted my daily workflow since upgrading. I work with alot of text. Reading other comments it looks like I can re-train myself to get around this? I never took the time to understand it- my muscle memory is too deep on this one.

Nice report!
I also noticed this, but quickly got used to it.
It's sad some people suffer from new approach, but it was highly probable, as always is with dropping old behavior.
I would try both solutions simultaneously.

This issue also occurs even if you click within a text box but are not over an actual text character. For example if you have multiple lines and click a few spaces right of a short line that is not over a text character, and try to start a marquee select from there. It will make a new text box inside your text box in that case.

In 2017 CC Illustrator (and 2016 I believe), I could marquee select text on a text box in scope to edit text. Now in 2018, any time I am working in a text box and click-down outside the scope of the textbox, it immediately exits the text box and creates a new one. This is problematic for me when I am working with text and want to highlight portions of text but need to start the marquee selection outside of the text and drag it in. It results in alot of redundant re-selection and very careful precision to avoid further de-selection.

This could be solved in a few different ways.

Proposal 1:
Don't exit scope of a text box unless the mouse-input has both clicked-down and click-released outside the scope of the text box without having selected anything while the click was down. This should alleviate my issue, while also solving the presumed problem others were having which initiated this 2018 feature change in the first place (i.e. others wanted to create text boxes easier with a single click out of scope). This could be the default functionality without causing any grief (probably).

Proposal 2:
Allow an option in the Type Preferences that allowed the user to set this back to how it functioned in 2017.

Video:
Here is a video of marquee selecting text in 2017. This is no longer possible in 2018, as described above.

https://www.youtube.com/watch?time_continue=12&v=b4OaCe42FMs