This problem affects both FileMaker 14 and 15. It's been tested on Mac OS 10.11.4 running on a late 2015 iMac 27" Retina.
I have a value list that is sorted non-alphabetically from a field's value by putting non-breaking spaces at the front of the value. The non-breaking space is Char ( 65279 ) and the field's language is set to Unicode. There are a couple of articles describing the technique here:
The field with the value list attached is being used in a find and it was returning 0 results in FileMaker Pro 15 when the file was hosted on FileMaker Server. Upon investigation, I found that the field's length is 1 character less than it should be. The first character is being removed when a value is selected in the value list.
If the value selected is Zebra with one Char ( 65279 ) in front of it, the length should be 6 but the hosted file returns the length as 5. If the file is opened locally, then it correctly returns the length as 6.
In FileMaker 14's WebDirect, it correctly returns the length as 6. Unfortunately, I can't test in FileMaker 15's WebDirect because it replaces Char ( 65279 ) with 'feff' which I believe has been acknowledged by FileMaker as an issue according to the comments in the above article.
I've attached a test file that shows the problem. Username: Administrator, Password: admin.