Problems when scaling a drawing using fractions

Hello,

I have a problem working with fractions while scaling objects in my drawing.

This is the situation:

My drawing is in inches and the scale factor is 1/8. When I insert blocks that are full size and in millimeters, I have to convert to inches so, I use the fraction 1/25.4 to scale to inches. Then I have to convert to the drawing scale, so I scale it again using the fraction 1/8.

I thought this was working fine, until it was pointed out to me that when I used 1/25.4 & 1/8 these factors did not work and the scale was not proper. My blocks were off and thus, my drawing was incorrect.

Why would this happen? Is it something that I am doing wrong or is it a bug in the program? Do I have a setting not correctly set? Please help, I do this kind of work daily and I have no idea how many files that I have messed up due to this problem.

Thank you in advance for your help!

Christina