Cannot get Script Runner function expression() to work with custom scripted fields

Created two sets of custom fields with one being a HTML formatted String and the other being the "raw" value equivalent. Both sets of values are calculated correctly without exceptions for all issues. The results are null for any non-Epic issue. There is only one config/context for the custom fields. The raw values are Longs returned as Doubles. They have a Number Field template and a Number Searcher indexer. I have re-indexed many times.

I need to create a filter e.g:

project = mine and issuetype = Epic and issueFunction in expression("", "EpicEstimatedRaw > originalEstimate")

However, every time I try to use this value I get the error:

Field EpicEstimatedRaw not found or not a Number or Date custom field.

I tried to use the "cistomfield_12345" format and got the same error.

Note, I can use the following filters successfully:
project = mine and issuetype = Epic and issueFunction in expression("", "originalEstimate > timeSpent")
project = mine and issuetype = Epic and EpicEstimatedRaw > 42129

I have seen a similar issue ( GRV-300 ). According to the issue this was related to locale. My locale is English (United Kingdom). Also according to that issue it was resolved and fixed in 2.1.10.