JQL search for few words not working without adding \ in front of " though the word is not listed in reserved words

Issue Summary

JQL search for few words not working without adding \ in front of "(quotes) though the word is not listed in reserved words

Steps to Reproduce

1. create a custom field (Navigate to Jira administration > issues > custom fields)with the name "Absatzmittler" of type "Text Field (single line)" and associated with all screens.
2.  change the indexing language and default language to "German" (Navigate to Jira administration > General configuration > Edit settings)
3. create 2 issues for the field "Absatzmittler" value contains DM and AM
4. try to search the issues like below using JQL like Absatzmittler ~ "DM" returns issues however Absatzmittler ~ "AM" is not returning any issues
   
   
5. try to search for AM with double quotes still, we couldn't search.
   
6. try with this JQL Absatzmittler ~ \"AM\" and finally it worked
   

 This is also reproducible when the indexing language is set to  "English - Moderate Stemming" and Default language set to "English (US)" & also with "English (india)"

Expected Results

both JQL queries Absatzmittler ~ "DM",  Absatzmittler ~ "AM" should return results

Actual Results

JQL like Absatzmittler ~ "DM" returns issues however Absatzmittler ~ "AM" is not returning any issues

Workaround

1. try with the JQL like Absatzmittler ~ \"AM\"  it works