It's not the added text that makes the link unclickable. It's the edit that makes the link unclickable.
Make a post containing a link with two spaces before that. After that, click on "edit" button and save the post without making any edit. You will see that the link becomes unclickable.
The same thing happens when the number of spaces before a link is a multiple of 2.
That's interesting. Btw, is this public knowledge and did you already know about this before you saw my thread or did you figure it out by doing your own tests? Any idea why it only affects empty spaces before links dividable by two and not all links for example?