I noticed the same thing this year, 2012, despite having the morning glory for the third season and in fresh potting soil. The leaves also attract a "bunch" of Daddy Longleg which do not seem to munch on aphids, so it has to be something else. The curly/crinkly leave has round black eruptions (for lack of a better word). Wonder if it is some kind of mold since the adjacent hydrangia flower also are turning black.

There may be a few Ipomoea purpurea in there , but most of those leaves look to be Ipomoea nil which tend to flower later than Ipomoea purpurea... They look to be in relatively small or thin containers...wonder how much water they can hold onto (that cement can get hot and baking) and if the upper part of the 'trellis' is getting adequate sunlight... The acquisition of any misidentified seeds contributes to myths about MG's because the person growing them doesn't really know what they have and are therefore somewhat working in the dark... There will always be people who have grown improperly identified species = unknown species and then make all sorts of claims about being so experienced with the 'horrors' of MG's although most couldn't accurately ID even 1 species if their life depended on it and urban myths are created and perpetuated e.g., (MG lesson of the day) there are Calystegia and Convolvulus species which do NOT spread by underground rhizomes...(!)... So , not all Calystegia or Convolvulus species are 'bindweeds' but there are University Botany Department Heads that don't know that (!) , although they have 'professional' websites up to guide the ignorant 'amateur/ layperson '.... Make sure you get what you are supposed to get as per seeds ( try and be sure they actually know what they purport to know) and make sure you get an accurate ID by someone who really knows how to tell the difference between the plethora (i.e. thousands !) of different species... Hope some of that helps... regards, Ron

Yes, it happens. It resembles what I have seen on leaves after the intense sun happens and burns the leaves.

based on the pic provided.. as well as your location .. and info about weather since spring.. and any other pertinent info ... i am unable to come to any conclusions .... ken