I found the mistake!
After doing some tests with all the possible options, i found out that only when the command was Xnnn with Tool 3 selected did the axis not move. When it was Wnnn it did move, either it it was absolut or relative, G0 or G1, heated or not heated.
That meant the X axis of tool 3 was not correctly mapped. And voila: "M563 P3 D3 H1 X6 F3", where the 6 had to be a 5.
Thank you very much for your tips and your help!