Hi - Working on a foreigner..My Kitchen

I've created drawings of all the parts using text file global dimensions. But it keeps loosing the link

For Example

- Carcase Back - Configuration 600wide - width ="Carcase_Back_Width_600" - From text file SW puts in (SUM)580mm - perfect

- Carcase Back - Configuration 500wide - width ="Carcase_Back_Width_500" - From text file SW puts in (SUM)480mm - perfect

- Carcase Back - Configuration 500wide - width ="Carcase_Back_Width_400" - From text file SW puts in (SUM)380mm - perfect

- go back to - Carcase Back - Configuration 600wide -width = dimension is still 580mm but has lost the link... WTF?

This appears to be random!

Any guidance please?

Thought it might be because I'm using Notepad++ - NO

Thought it might be because text file was open at same time as part -NO

Thought it might be because the dimension was driven by formula - NO