Why does SourceTree tell me no changes detected for unstaged files?

[Anthony Gibbs]

SourceTree is correctly listing the files I've edited, but when I click on any of them, the internal diff area says "No changes in this file have been detected, or it is a binary file or it is configured to be ignored by the File patterns", and then opens a CodeCompare window which correctly displays the changes that were made.

Note my files are not binaries, and the File pattern settings are correct.

This started happening about two weeks ago. I have uninstalled, and then upgraded to latest version, with no change in behaviour; this makes SourceTree borderline unusable.

I have run

git config set diff.tool ''

in the hopes of stopping this, to no avail. Any ideas?