I consulted extensively on this and I'm copying over the response I just gave to the other blank line question that came in just before yours. That question is almost identical to yours and raises the very same issues. The person was asking primarily about the bottom box line, but the answers applies to all formats that require a blank line before and after and how that relates to the page turn indicator. This is the response I gave:
I suggest a trip over to Appendix C Blank Lines. The appendix does try to pull together and summarize wide-ranging topics, such as this one.
The new concept in Formats 2011 is that the page change indicator does not change anything about the use of blank lines UNLESS there is more than one format involved.
The bottom box line ends a print page. Since a blank line follows a box, there is a blank line between the bottom box line and the page change indicator. BUT if that next print page starts with a cell-5 heading, which requires another blank line, the first blank line, after the bottom box line, is omitted and the page change indicator follows immediately, followed by a blank line and the cell-5 heading. And yes, it is true that there is no exception listed in 7.2.1b, but 1.10.3c and Appendix C both say that in such cases, when two blank lines are required across a page turn indicator, the first blank line is omitted.
This same situation is true for lists and for any format that requires a blank line before and after.
The easiest way I found to see this is in the Sample 8-2. This has to do with lists, but this works for boxes as well.
At the end of the print page, look at the format that comes after the ending box, or list or whatever. Does that next format require a blank line preceding? If the box is followed by a plain old indented paragraph or something that does NOT require a blank line, the box (or list, etc.) has a blank line followed by the page turn indicator. Sample 8-2 shows this.
If the NEXT format requires a blank line preceding, then omit the blank line BEFORE the page change indicator.
Please let us know if this can be clarified further.