Scroll problem

Situation 1:

I preload a txt-file into a dynamic field. When I push a button==> no problem, the file is loaden into the field!!
Now when I insert in this field a scrollbar and Test Movie do, the txt-fiel will be loaded, but the scrollbar remains disabled.
How does this come q:

Situation 2:

I copy and paste the txt-file into the field and Test Movie ==> No problemo, the scrollbar works:-s

Does somebody has an explanatiuon for my problem?

Many thx