steps to reproduce:
- create a new text file
- insert a section, make it 2 columns
- insert text to columns
- below section:
- insert other text
- insert data fields (does not matter where from, in my case a simple csv
(attachment 2 [details]) with only one row after headings suffices)
- save (attatchment 1)
- choose print
- a dialog pops up, saying doc has mail merge fields, choose yes to merge
- select: all, save merged document to single file, ok
- open merged document

expected:
layout should be preserved, double column section in every merged page

found:
your section is gone (but its contents is there), the whole document is single
column (attachment 3 [details])

I noticed this behaviour already with 2.3.0 and 2.3.1, maybe earlier

workaround is:
save to multiple documents: layout / section kept
print directly: layout ok

very unhandy if merging a big number of datasets and wanting to review / edit
the merged documents before printing