I am currently getting similar results when I edit a recordset. Even if I just open the recordset from the server behaviors panel and close it without making any changes, the recordset code is duplacated. I have got used to having to go to code view and removing the extra code, but sometimes I forget - and am only reminded of it when I upload the page and get the error message,
"Fatal error: Cannot redeclare getsqlvaluestring() (previously declared in /home/hackers/public_html/ue4/index.php:25) in /home/hackers/public_html/ue4/index.php on line 85"
This has only been happening fairly recently, so I am not sure what the catalyst is. All that I have added is UE4, but - as you say - recordsets are a DW functionality, but I can't see that opening a dialogue with Adobe would help too much as I have not updated DW itself in any way. I'm guessing it's (my) user error I suppose, but I just can't work it out why.
Have made a 2 page DataAssist page-set (results, Delete) to demonstrate.