Thank you for your post.
The drop-down value list works the same in WebDirect with FileMaker Server 13 and FileMaker Server 14. If you set the value list for "Auto-complete using value list", the value list will be filtered by what you type in. However, in WebDirect, the value list will not auto-complete like it does in FileMaker Pro.
Since this is not working for you, let me know how I should set up a value list so I can replicate the issue.