Table Merge Cell Issue

I have found what appears to be a bug in the merging/unmerging cells feature in InDesign tables.

Background: I am currently working on an 85 rows by 5 columns table that also includes a row header at the top. I am making a schedule, and am merging rows together for the events in that schedule. I want to be able to edit these tables in the future, so I want to preserve my ability to unmerge any of the merged cells I want to without impacting the underlying number of rows/their size.

The issue: I am able to do that except in one case—when I merge parallel rows in each column. What I mean by that: when, for example, I merge rows 2-4 in column 1, then separately merge rows 2-4 in column 2, then 3, then 4, and then 5. Once I merge the final rows in the last column (but not before), InDesign then switches from treating each of those events as three merged rows but as one row. I am no longer able to unmerge any of the rows, unless I hit cmd-Z. Furthermore, if I go to table/table options/table setup, it suddenly says I have 83 body rows instead of 85.

As I have some events in my schedule that are the same each day of the week, I need to be able to merge the same rows in all of my columns without InDesign changing the fundamental structure of my entire table.

Any and all help is appreciated! Please feel free to ask clarifying questions—this issue is slightly difficult to explain over text only.