Sheet scale is off

Hi, I have two drawings from different companies. Sadly, they draw with different standards - e.g. the dimension formatting is very different. If I try to draw something myself to them, I have to amend manully the styles. But the biggest problem comes from the sheet views. When I import a block with attributes as a 1:1 scale it imports HUGE. Yet, when I import into another drawing it comes corretly. When I import the block into an empty drawing, this is also fine. 

The "huge" drawing sheet tab just seems out of scale. 

Here's an image. The sheet is A4, the line behind there is drawn as 50mm, yet it is way out of the borders.

What am I missing?