REQ: How to remove a style which has no name?

Checking a file with BE it throws me the error "Style has no name! This style has no name, and so won't appear in the style list, even though it exists in the file.  This is a bug in FileMaker Pro, and there is no simple way to clear out the style as it can't be located.  They don't cause problems, but do take up a small amount of space.  You can try saving the style changes or the theme to clear these out."

But neither saving all Styles on all Layouts nor saving or renaming the Theme works.

Does anyone have any idea how to fix that?
 

TIA
pixi

This is the xml coming from the DDR:
 

Quote

<Style name="">
button_bar_segment.FM-1B2E9EF7-7DC2-44F7-AF3D-63E62E75A073:normal .self
{
background-image: none;
background-color: rgba(100%,100%,100%,0);
border-image-source: none;
text-align: left;
-fm-text-vertical-align: top;
}
button_bar_segment.FM-1B2E9EF7-7DC2-44F7-AF3D-63E62E75A073:hover .self
{
background-image: none;
background-color: rgba(100%,100%,100%,0);
border-image-source: none;
}
button_bar_segment.FM-1B2E9EF7-7DC2-44F7-AF3D-63E62E75A073:pressed .self
{
background-image: none;
background-color: rgba(100%,100%,100%,0);
border-image-source: none;
}
button_bar_segment.FM-1B2E9EF7-7DC2-44F7-AF3D-63E62E75A073:checked .self
{
background-image: none;
background-color: rgba(100%,100%,100%,0);
border-image-source: none;
}
button_bar_segment.FM-1B2E9EF7-7DC2-44F7-AF3D-63E62E75A073:normal .inner_border
{
padding-top: 7pt;
}
button_bar_segment.FM-1B2E9EF7-7DC2-44F7-AF3D-63E62E75A073:focus .inner_border
{
box-shadow: none;
-fm-box-shadow-persist: inset 0pt 0pt 2pt 1pt rgba(0%,43.9216%,81.1765%,1);
}
button_bar_segment.FM-1B2E9EF7-7DC2-44F7-AF3D-63E62E75A073:normal .icon
{
background-position: left top;
-fm-icon-color: rgba(76.0784%,76.0784%,76.0784%,1);
-fm-icon-padding: 20pt;
}
button_bar_segment.FM-1B2E9EF7-7DC2-44F7-AF3D-63E62E75A073:hover .icon
{
-fm-icon-color: rgba(76.0784%,76.0784%,76.0784%,1);
}
button_bar_segment.FM-1B2E9EF7-7DC2-44F7-AF3D-63E62E75A073:pressed .icon
{
-fm-icon-color: rgba(76.0784%,76.0784%,76.0784%,1);
}
button_bar_segment.FM-1B2E9EF7-7DC2-44F7-AF3D-63E62E75A073:checked .icon
{
-fm-icon-color: rgba(76.0784%,76.0784%,76.0784%,1);
}

</Style>