Ok i've found an example
In this particular case Validator missed a note reported by Toolbox. When I looked into the code, both Toolbox and Colour Highlight did not detect tile load properly and they both used a timer to periodically re-highlight segments.
So I had to implement a trick in Validator: once it detects the tile is loaded and ready, Validator dispatches an event to WMECH to force it to re-highlight the segments. It does not send anything to Toolbox though and I don't remember the reason. Probably the trick didn't work with Toolbox or smth
Generally speaking, those misses are plausible in Validator, esp. for the very long segments crossing the map view. So few month ago I send a message to Ohad asking a permission to use a low-level WME calls. It would allow Validator to scan the map few times faster and detect issues on the very long segments.
Now the validation functionality being implemented on the WME servers, I guess there is no reason to put much efforts here...