Replace (CTRL+R) adds/replaces extra characters when the character to be replaced is followed by "." (i.e. dot). Options in AutoBrace, i.e. "Automatically add closing brackets" and "Automatically add closing quotation marks" must be enabled as per needed before reproducing the bug. 

Reproducible: Always

Steps to Reproduce:
Case 1: 
1. Enable "Automatically add closing quotation marks" but disable "Automatically add closing bracktes" in AutoBrace
2. New file
3. Input '.b' (i.e. a dot and the character"b", enclosed by a pair of single quotation marks)
4. Press CTRL+R (i.e. Replace)
5. Find: '
6. Replace: "
7. Mode: Plain text
8. Press "Replace All" button (or "Replace" button twice)

Case 2: 
1. Enable both "Automatically add closing quotation marks" and "Automatically add closing brackets" in AutoBrace
2. New file
3. Input [. (i.e. a left square bracket followed by a dot)
4. Press CTRL+R (i.e. Replace)
5. Find: [
6. Replace: (
7. Mode: Plain text
8. Press "Replace All" button (or "Replace" button twice)


Actual Results:  
Case 1: 
"".b""
Case 2: 
()

Expected Results:  
Case 1: 
".b"
Case 2: 
(.

Possibly related: 
https://bugs.kde.org/show_bug.cgi?id=342466