Bug report on attachment search in dovecot fts plugin

Hi.

I am using dovecot's fts plugin and have found a bug-like behavior.

I have confirmed that dovecot by itself with fts plugin disabled works fine.

dovecot --version 2.3.19.1 (9b53102964)

The pattern we found is as follows

1. search with with attachments condition from RoundCube linked to dovecot
2. dovecot fts plugin executes the following query to solr but no document is found hdr:application%5c%2f+OR+hdr:multipart%5c%2fm+OR+hdr:multipart%5c%2fsigned+OR+hdr:multipart%5c%2freport
3. roundcube search results also show no items found

That's all I have to report. If there is any way to improve the situation, we would like to receive it.