What version are you running?
SW2014 introduced a handy feature that scales your entire sketch when you place and type in the value for the first dimension of a sketch.
"This never happend before." You never did it before!
You have not displayed the sketch relations, so we can't help you, but my guess is that because the top line is black, you have Fixed it.
John is probably right about that horizontal line being fixed. The only other possibility I can think of is if the dimension is set to "Driven", but I doubt if that's the case because then it would almost certainly be gray instead of black
Post your file with the sketch..... Use the Advanced Editor link in the upper right of the dialog box.
Sketch behavior has changed in SW2014. Your sketch will proportionally scale the entire sketch when you place your first dimension.
Without seeing your file it is hard to guess if this is what you are seeing.