OH 3 Sitemap Frame in Frame

Hi all.
I am on openHAB version 3.1.0 Build #2107 building sitemaps.
Sitemap configuration with a Frame in a Frame

File based Sitemap

sitemap test label="Home" {
    Frame label="" {
        Text label="Kalender" icon="kalender" {
              Frame {
                  Text item=Muellkalender_Ergebnistitel1 label=""
                   Text item=Muellkalender_Ergebnisstart1
              }
        }
    }
}

look like this

Main UI Sitemap

sitemap page_44b83db136 label="Home" {
    Frame {
        Text label="Muellalender" icon="trash"
        Frame {
            Text icon="trash" item=Muellkalender_Ergebnistitel1
            Text item=Muellkalender_Ergebnisstart1
        }
    }
}

sitemap1

look like this

Do i miss something in Main UI?

Rolli