Why is SVN merge not tracking merged revisions?

The most likely answer:

The URL to merge from is case-sensitive. If you merge from a URL with the wrong casing the merge will work for the files but the revision will not be recorded in the MergeInfo property.

This can be a frustrating problem because SVN and TortiseSVN do not give any feedback/notification about the mis-matching urls during a merge.

How I figured it out

Recently, my svn client merge-tracking stopped working. I was performing merges with TortiseSVN at the root level but the revision numbers where not being recorded in the MergeInfo Property. There were no error messages either.

I then tried merging directly with svn from the command line but got the same result. No error messages either.

It was not until I thought to try to do a merge from the command line with the --record-only option. This was the only command that provided an actual error message:

svn merge -c 16304 https://server/svn/project/trunk/ --record-only
svn: E200004: Merge from foreign repository is not compatible with mergeinfo modification

Once I had a meaningful error, I was able to track down this old forum conversation (argument) about case sensitive urls and TortiseSVN.

I hope this saves you some time.