RadImageEditor for WPF provides support for TIFF/TIF images from 2015 Q3
release. So, it is normal a tiff image to not be imported at all in previous versions.
If you are using a custom image provider, the issue might be caused by that exact image, or because of an issue in the implementation. However, it will be much easier for us to investigate and find what might be the issue if you send a sample demo project with the corresponding image attached where the issue is reproduced.
Looking forward to your reply.
Do you want to have your say when we set our development plans? Do you want to know when a feature you care about is added or when a bug fixed? Explore the Telerik Feedback Portal
and vote to affect the priority of the items