This problem is quite annoying, but you can get along with it. As UhelligGudn said its 2 seconds, that time usually doesn't really matter, but only if you are not in combat. Inside a combat it can really change the tide, so just make sure you are in the mode you want to be if you enter a fight.
But I'd really like to see Stardock makeing TB respawn in the mode he died in.
Does it really matter that much? It's free to change modes and takes a whole 2 seconds. Not to mention it makes a little more sense to respawn in ice mode since thats technically his "normal" mode, as he walks around normally and such, whereas his firemode, he is flying and all that. Seems "logical" that if you died, you'd be forced into normal mode again.
Technically, it is like you said, ice mode is his "normal" mode, so he respawns in that mode. It's the only logical thing to do if you don't say the game that it has to do something else. Probably thats the reason for it being like this now. But that doesn't really make it more logical. Normally dead things stay dead, so you cant really add a logic to someone respawning.
The whole thing really matters. It's not that important at the moment, but if you go 100% fire without a single ice skill you have to wait an extra 2-3 seconds for nothing but changing the mode, so you could say that a fire TB got a longer deathpenalty than the other demigods. Considering that the deathpenalty usually is only in second range it is quite a lot time.
It's a bit of a non-issue tbh. It's like complaining that UB doesn't have Ooze active when he spawns after dying with Ooze active.
It's not really like that.
Ooze dosn't give you a new set of acitve skills you maybe don't even have. Ooze is instant. (iirc)