I have done all my fruit in the oven for many years and have never had any problems whatsoever, nor have I ever had a problem with jars breaking or fruit spoiling, ever. My family has never fallen ill from oven canning.
I do put the lids on jars before putting them in the oven and only when bubbles start rising, do I consider them canned. By the time I finish emptying the oven, the jars are already popping to indicate they are sealed. None of the testimonies I have read give any detail as to what ill effects result from oven canning and I would like to know what sort of problems people are encountering.
It's difficult to know if all the heat in the oven is evenly distributed and thus, each jar is completely and evenly heated to kill the bacteria and germs. The lids' popping down is not an indicator of safety. All it indicates is that the contents of a heated container are cooling.
Please use a pressure canner for low-acid foods and a pressure or boiling water bath canner for high acid foods and follow the directions in the latest Ball Blue Book or from your county extension or the USDA.