When METL melts into lava, it creates pressure. When the metal begins to solidify, this pressure pushes the remaining lava upwards a bit. Maybe use PUMP with temp 0 to equalise the pressure (IDK, I haven't tried this).
In any case, this happens to all materials that melt into lavA.
Turn off pressure in the settings menu.
solutions:
1. press the moltenmetl with something like ttan
2. turn air completely off
Pour it into a mould made of GOO then use pressure to melt the goo away.
-for driffent posts-
pound the lava with a stronger pressure/pulling it into a single place/vaccum in bottom of the smeltery.\
lava, in the powdertoy, are SUPPOSED to gentrate pressure. and, molten metl are ctyped lava(try setting lava's ctype to metl, and the it says molten metl), BUT, since metl is solid, the lava blows away and when it becomes solid again(the lava's temp is lowered, lower than metl's ), it is stuck in one place. because the lava is split, when it solidfies it looks like its curled.
Before it curls, flash-freeze it with CFLM or NICE or Liquid Nitrogen.