Maybe this category adequately covers it.
Good enough, @duncan, and likely correct, as my story below confirms.
My prompt was because I had what seemed attributable to v4 upgrade. I was curious if others were having similar problems (pages expanding upwards of 100 times! in length–3000px-> 300000px). After looking through all the various threads, even reading some from two and three years ago, I saw nothing associated with v4. This is the point in the story where I suggested the “New Versions Issue” topic.
Eventually I dug out the backed-up pre-update file and compared it with the v4 file. The issue was NOT in the transition file, and opening the backed-up backup file in v4 did not re-produce the error. Thus, conclusively, the page length expansion was NOT part of the v4 update even though at first blush I suspected it was. Turns out the expansion occurred while I worked on moving posts between different blogs, creating the post summaries, and making the posts responsive. Somewhere in there the footers and page bottoms became crazy (in the blog sections and most others). Oh, I was also futzing around with menus for different sections. Yes, I know, I need a more focused work flow .