.csv data save does not really work on multiblock data and there is no warning
When you try to do a "save data" with .csv data, or do a catalyst script with .csv export, the output is not useful if the data is multiblock--you have to do a merge blocks first to see useful info. The user should probably get a warning about this and be informed that they should consider adding a merge blocks filter. Taking the data type (.csv) out as an option when you are saving the data and it is multiblock might be acceptable, but it would be helpful to the user to know he or she could do a merge blocks then output .csv data. Another option might be to output cell data recursively descending through blocks, and add a block id column to the .csv data for cells (and points?).