I am not sure on the way you develop the test the product before releasing it. The issues what i faced were very peculiar in case. Base functionality almost changes from version to version and i dont understand why.
Lets see the case what i found below.
I have a SL 3.0 application hosted in sharepoint. And i upload files to the sharepoint doc libraries from silverlight. My XAP File is placed in a sub folder in Layouts folder of 12 hive of sharepoint. This XAP at run time looks like http://<site>/_Layouts/<subfolder>/<XAPFile
I have specified hanlder URL as ~/Handler.ashx and placed the handler in the root of site as ideally ~ takes root.
When i ran this XAP with different versions of RAD controls in one version it tried to find the handler in the path /_Layouts//http://<site>/_Layouts/<subfolder>/
and in the other version it pointed to the corrent path which i http://<site>/Handler.ashx
. This looks so small but it is irritating as RAD upload conrol just shows error icon in control but doesnt show any error in either tooltip or control when it is hosted in sharepoint. This has delayed our UAT by 2 weeks.
Now onwards i will be very careful when i am using RAD.