rbelknap wroteI was having a weird problem using a document link. I had selected URL as the datatype and used the link type of file on my site. I uploaded a file named 09.
08.06.000004.pdf. I then realized that I had made a mistake and used the dnn file manager to rename the file to 09.
09.06.000004.pdf, but when I returned to the UDT list the link still showed as 09.
08.06.000004.pdf. I tried clearing my cache.
The URL datatype stores the relative path to the file and not a pointer to it. This is different to the Download type which stores the fileID. So renaming inside dnn file manager will not change the name inside udt and the old but wrong name is shown but the link should be broken.
rbelknap wrote
This did not work so i tried deleting the record and redoing it with the renamed file and got the same error. I deleted the file and the record, uploaded the file via ftp and recreated the record and even though I uploaded and selected a file named 09.09.06.000004.pdf the link displayed as 09.08.06.000004.pdf
I then tried changing the file name to another file called instructions.pdf and the link was correctly changed to instructions.pdf. This worked so I thought I would reselect 09.09.06.000004.pdf and be good to go... no luck it still showed as 09.08.06.000004.pdf.
Sorry, I can not reproduce this issue with DNN3.3.4 or DNN4.3.5(internal beta). If I rename a file with the file manager it will not work any more. If I edit this row, the url control will show it as not specified and I can select the nrenamed one and everything is fine.
Do you really use the URL datatype? I can reproduce your issue using the download datatype inside DNN3.3.4. It is a caching issue and you can not solve it with clearing your cache - an iisreset would help 
DNN4.3.5 works perfect. All I can say is that your issue is not caused by UDT but DNN UrlControl. Please tell us your DNN and UDT version.