To reproduce:

• Have a Mana-storing item (Tablet, Band, Greater Band) in the top-left inventory slot (inventory slot 10).
• Have some way to charge the Tablet in-place (Band of Aura or Dispersive Augment).
• Have a smeltery with a capacity of at least ten items.
• Put something meltable in the tenth slot of the smeltery.
• Let it progress a bit, then close and reopen the Smeltery Controller while the Tablet is being charged.
• The melting progress (orange bar) of the tenth slot will reset to zero.

The affected smeltery slot depends on which inventory slot the charging Tablet is in. Move the Tablet one slot to the right (slot 11) and slot 11 of the smeltery is affected instead. Bands of Mana (and Greater) still cause the issue. Does not occur for slots 1-9 (the hotbar), nor does it occur for Bands in the Baubles slots. On occasion, a Tablet (or Band) will briefly appear in the affected smeltery slot.

Forge 10.13.2.1272
Botania 1.3-144
Tinker's Construct 1.8.0

Closing in favor of SlimeKnights/TinkersConstruct#1244

I.... wot

0_o

Ehmm... ok?

Wait What how is that even possible?