[repeat] mouse icon during application startup

[<test_account tutanota de>]

Hi, I asked a question about this problem yesterday but obviously nobody understood what I mean so here is an image: https://cdn.mediacru.sh/i/iKibSNh1S0oJ.png

this is the mouse icon that shows up every time gtkmm application is started.
Why? and what to do to get rid of that icon?

I'm developing with other libraries too and have this problem only with gtkmm applications.
Why is this happening?
Thank you!
~Brute