I couldn't reproduce this, but I've fixed 3 'issues' in:
https://github.com/ocproducts/composr/commit/d1944e9556bed0d289f55e8aab094278be70fc05
In order:
1) The first is a real but tiny bug, broken breadcrumbs on the "do next" screen after editing a template
2) The second is related to the only cause I could think, which is a possible hole in the logic that customises the path. I can't think of how this would fail in practice though.
3) The 3rd is making sure the MAIL.tpl editing link includes "templates/" on the front, which is a new convention in v10.
https://github.com/ocproducts/composr/commit/d1944e9556bed0d289f55e8aab094278be70fc05
In order:
1) The first is a real but tiny bug, broken breadcrumbs on the "do next" screen after editing a template
2) The second is related to the only cause I could think, which is a possible hole in the logic that customises the path. I can't think of how this would fail in practice though.
3) The 3rd is making sure the MAIL.tpl editing link includes "templates/" on the front, which is a new convention in v10.