Troubleshooting / Bugs: Using regex with Search & Replace (0.3.1.547)[Solved]

I’ve been testing out the regex in the search and replace and I’m having a problem with using back references.

I’m using some pseudo text (see below) and what I was trying to do is swap the places of the letters with the numbers.
I tried using: ([\w]+)_([\d]+)$ for the search term so the letters should be the first back reference and the digits should be the second back reference. But when I put:
\2_\1 as the replacement text it doesn’t work as I’d expect. Have I overlooked something or is this a bug?
Any insight would be appreciated.

Pseudo text:
foo_1234 bar_1237 foobar_3244 foo_2352 bar_2362 barfoo_1213 foo_6472 bar_7832 foo_8293 bar_3609 foobar_1239

Result Text:
2_1 2_1 2_1 2_1 2_1 2_1 2_1 2_1 2_1 2_1 2_1

• Regex ref

Edit: I just noticed an error with the “Preview Post” when previewing a post it requires you to escape backslashes in order for them to show up but when you make the actual post all of the slashes appear.

Ah works :) Thanks.