You are not missing anything, blindscan should not have anything to do with T2-MI, since the reception of these channels is not done directly when searched but through decapsulation. Now what Enigma2 is forced to do in this case is search and decapsulate at the same time. Perhaps it could be possible with more code optimization (although highly unlikely) but it's not necessary. In my opinion T2-MI blindscan should be disabled, and activated only through manual search with given parameters.
In this case, blindscan finds the T2-MI frequency parameters, but it's impossible to find the necessary pid through blindscan, as this requires a search in the SDT tables too, which will slow down the scanning considerably.
As a workaround to this, perhaps an optimization of code with syncing and adding the T2-MI parameters in the found transponder with sync known transponders function should do the trick, but I don't know how feasible that would be since it will mess the scan on all other receivers except Octagon.