Problem with time dependence initial conditions

Hello all,

I am trying to do a very simple model of 2 iron blocks in thermal contact where their initial temperatue value is T=0C and only one side (boundary) of one of the blocks is set to T=100C with the "Temperature node". The rest of the faces are thermally insulated.

I do this study as a time dependent evolution, but one thing I noticed is that at t=0 the temperature profile where the boundary is set to 100C is NOT sharp, but has a finite penetration inside the block.

Do you know what might be the problem?

Thank you!