Loki's Mischief - bug or planned?

Playing against Loki.

I hit a match 4 with him and it activates - ok.

I match 3 against him and I get a cascade that forms a match 4 and it doesn’t activate.

Only triggers when you make the first match or bug?

Was the match 4 on TU tiles? It doesn’t activate on TU tiles.

I guess it could have been…