Suppose a pie dish was used only for making fruit pie, and has never contained any dairy or meat.
Suppose it spends time cooking inside an oven that also contained chicken and meat.
The question is, can such a dish be put in an oven in which dairy (i.e. lasagna) is also being cooked?
What does Shulchan Aruch explain about this case. I understand that a specific real case should be brought to a LOR if there is a practical real question to be decided.
You asked for sources. See Yoreh Deah 95. Responsa Maharsham vol 3 si 208. Igros Moshe YD vol 1 si 40 and Minchas Yitzchak vol 5 si 20 see also Badei Hashulchan si 92 s 8 in biurim.
When placed in the oven with meat, the worst that can happen (assuming there was liquid with the meat and it is uncovered) is that the pot absorbed meat flavor. This doesn't render the dish meaty but you cannot eat it together with milk a priori - however you can eat milk afterwards without waiting six hours.
The pot however doesn't become meaty. Therefore one can place this (still parve) pot in a dairy oven with lasagna.
Since there are permutations of these cases, it is important to ask a rav.
For sources, see details in this answer.
