Lowercase abbreviations such as 'Bout, 'Cause, 'Em, etc

I want an action to lowercase abbreviations such as 'Bout, 'Cause, 'Em, etc. to 'bout, 'cause, 'em, etc. I thought I had it solved but now it doesn't work for some reason, perhaps because \b doesn't work in all files(?).

F=TITLE
1=\b'(Bout|Cause|Em|Fore|Long|N|Round|Til|Till|Twas|Way)\b
2='$lower($1)

Could you show us the cases where it does not work?
MP3tag has a preview function in Converter>Tag-Tag where you can test scripting functions like $regexp().

If all that does not help, you could try alternatively an action of the type "Format value" or the already mentioned converter Tga-Tag and the scripting function $replace() in which you replace the upper case words with lower case ones.