Sorry for the double post...
At least does it at the start of a new game. I will try a time and report...
This debug function is very good, you just have to make sure, in the case of adding new GRFs, that they are compatible with those already activated.
The dev's constantly talk about issues and corruption but I've never had any issues in the 10 years I've been playing OpenTTD, just so long as you dont change anything your using while playing (Like removing a trainset your using cars and engines from) or changing industry sets (that'll really make things weird with lots of missing sprites and <invalid cargo> popping up everywhere)
If you run into any crashes or issues after changing NewGRF's your very unlikely to get support from the dev's, though I'm sure that others may help at least and figure out if an issue is because of changed NewGRF's in a game or scenario, or if its something else.
Plus I think its silly that changing GRF's in scenarios is disabled by default as most scenarios are devoid of NewGRF's despite being based on a region or country that may have vehicle sets for that (like adding NARS+NARS Add-on to the USA Scenario)