It seems that tmru does not merge with existing entries when storing the mru list into a file.
This results in missing entries when multiple instances of Vim are running.
I could provide a test case if necessary, but basically you have to write to files in both of them, and then quit one instance.
The fix might be to read the existing list before storing/saving (similar to what wviminfo appears to do).
Improved synchronization of mru lists across multiple instances of vi…
…m (fixes #26)