I have already reported a similar issue (see link below), but now I have found another condition that gives different output for apparently no reason: simply changing page orientation.
I created two almost identical word documents (using Word 2013), with the unique difference that in one document page orientation is portrait and in the other one is landscape, then I executed the same C# code on both documents.
You can find 4 test tables in two the documents.
In the last test table, the cell with content “Very long label text” is merged for portrait, but not for landscape, in both DOCX and PDF, but only if UpdateTableLayout() is not called (caling it the cell is never merged).
For other details, please see the main bug report:
Tested with Aspose.Words 20.3 and Word 2013.
Bug Dynamic Columns - Portrait vs Landscape.zip (111.1 KB)