This week is the somewhat rare Shabbat Rosh Chodesh Av. When that happens, we always read the section containing Numbers 33:38 about Aharon's death on Rosh Chodesh Av. In most communities this week a double portion will be read, placing that calendrical coincidence well over halfway into the reading. However, even more rarely in leap years (next in 5812 and 5839) the weekly reading for Shabbat Rosh Chodesh Av is just the section Mas'ei placing that calendrical coincidence well within striking distance for the first reader.
When Mas'ei is read alone the first reader generally reads until after verse 9*, but years ago when Mas'ei was last read alone on Shabbat Rosh Chodesh I recall a local rabbi announcing before the Torah reading that due to the rare calendrical coincidence, in order to have Aharon's death be read by a descendant of his, the first reader (a priest) would read all the way up to verse 50.
*I know that some communities rearrange the printed section breaks whenever Mas'ei is read alone in order to not interrupt the list of 42 encampments (MA to OC 428:6), but this is generally done by having the first reader read only 3 verses and having the second reader read until verse 50. There may be other variations out there which have the priest read to verse 50 always, but nevertheless that isn't the practice asked about here.
Can someone point me to any information about this practice? Which communities follow it? How old can it be documented?
