Custom Blob Brush changes to basic stroke after back/forth-switching to another tool in Ai 2019

Hey there, out of nowhere the blob brush stopped working properly as it did for the last years: If I use the Blob Brush with my own brush stroke and switch forth to another tool to delete something, coming back to the Blob Brush, it changes to the basic stroke. That means I always have to click on my custom brush again. Thats bothering. Is it a bug?

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