Calculated column being cleared when loaded to powerbi.com

I have a calculated field that comprises of the town a property is in with ", England" appended to the end to enable me to map the number of properties in each town on a Map.

This was working fine until recently, but it now appears that this field is being cleared (or not calculating), I'm not sure which, when I load the report to powerbi.com.

The visualisation works perfectly OK in the Desktop app and I cannot recreate the problem there, so it seems to be something to do with the Service.

Is this a known problem (a quick search with my favourite search engine doesn't bring anything up) or can anybody give me any pointers as to how to debug what is going on?

I have tried renaming the field from Country (in case that caused a problem) and I have dropped an extra visual onto the report which shows the list of towns and a count, but that is clear by the time the report is viewed on powerbi.com.

Somewhat puzzled of Peterborough!

Ian Watkins