If I type a /longsttring and correct it to /longstring, Text Blaze will FAIL to substitute the snippet. To work properly, I cannot miss a single character.
Why is that?
Hi, and welcome to the forum! 
Text Blaze does support backspacing and retyping characters if you make a mistake while typing a snippet shortcut.
It does not support changing the location of your cursor and then continuing to type the shortcut. Doing that would make it much harder to differentiate between when a user is typing a shortcut (and we should replace it) and when a shortcut happens to appear in a doc (but shouldn't be replaced).
So if you make a mistake in the future, you can backspace until you've deleted the typo and then type the rest of the shortcut.
Great, good to know the proper way! Thanks.