container field: calculated path name gets modified while writing to disk

Issue report by Carl Lofthaus

Product

FileMaker Pro

Version

14.0.1

Operating system version

Mac OS X Mavericks & Yosemite

Description of the issue

I want to store container data, mostly PDFs, in folders on disk, referring to related projects. This file structure has grown over the years and always starts toplevel with a folder named by the year, continued inside with project folders, that also start with year and month indentifiers, like:
2015/2015.10 project x/subfolder

Data should be stored externally (Open storage)

The path is calculated correctly and content will be saved to expected location, but writting content to the disk, it always ends up as:
2015/2015_10 project x/subfolder
replacing the dot with an underscore.

Is there a method to force a dot being written rather tha the underscore?

Steps to reproduce the problem

calculated field (path) value:
2015/2015.10 project x/subfolder

written file path:
2015/2015_10 project x/subfolder