Can't Drag and Drop between eM <-> eM or eM -> Thunderbird

Hello dear ones,

I can drag and drop messages from Thunderbird into eM Client (V8 Windows). Cool.

It does not work from eM Client to Thunderbird.

But above all: Even if I start eM Client 2 times (1x without parameters and 1x with parameter
“C:\Program Files (x86)\eM Client\MailClient.exe” /dblocation “C:\Users<username>\AppData\Roaming\eM Client OLD”
I can’t drag messages from eM Client (Old Database) to eM Client (New Database).

Does anyone know a solution for this?