This is working as designed. Web Access is designed to display no more than the first 10000 entries in a dynamic field dropdown, to avoid potential performance concerns of loading large amounts of data (which had occurred in the past when there were tens of thousands of entries at play). So the message is not an error, just a message to the user that there are other possible values aside from those listed. You should be able to set those values, however.

With respect to the description of the selected row changing when pausing for too long in typing in a value, that is expected behavior for an HTML drop-down field. What Junaid described would certainly work except that if this is a dynamic field, even text fields are converted to HTML drop-down fields. Whether there is a way to enforce an HTML text field or if not, whether it would be supported, I personally cannot comment on, but someone else might.

Hope this is helpful.