Conditioning phase temps

I currently have a porter that has been sitting in my primary bucket for 12 days. It was sitting at ~65 for the first week or so. Then I went out of town for a few days and while I was gone the temp dropped to ~58. Primary fermentation had already finished and my beer was in the conditioning phase. I was wondering if the low temp could cause any problems or off-flavors in my finished product? Thanks.

Nope, the esters and phenols from yeast production occur mostly during the first few days of fermentation. Many folks utilize cold crashing at much lower temps than 58 to "clear or brighten" some beers. The only thing I can think of would diacetyl, but the yeast probably didn't produce that much at 65* and could have already cleaned it up furing the week if it had.

when primary fermentation drops off and stops creating heat from within, my carboys tend to drop well below the recommended fermentation range (like 5 degrees below or more). i never notice a problem from this. everyone i know who has a keg system cold crash their beers before kegging. i don't know what temp they do it at but, as copbrew mentioned, it's well lower than 58.

edit: talking out of my ass

If you reached FG there will be no issues at all, lower temps simply help to promote yeast flocculation.