There is currently a bug where the elapsed time of archaeology casts becomes increasingly negative, because completedcasts in Tradeskill.lua is incremented but never reset.

The issue is that when UnitCastingInfo() is called for an archaeology research, it returns true for isTradeSkill, but it doesn't actually use DoTradeSkill(), so the counter of completedcasts is never reset. The value of completedcasts still properly resets when a cast of a profession that uses DoTradeSkill() occurs.

In the recording below you can see the elapsed cast time go deeper and deeper into the negative, until an engineering cast is started, upon which the elapsed time of the next archaeology cast is fixed.