Merge Across emptied the value and formula of the other cells in each row but
left their Python code, so a hidden cell stayed a Python cell with an empty
value and was saved as a PY formula. It now clears their whole content, as
Merge Cells and Merge & Center already did. In the same command, a merge
change evaluates again the blocked arrays that could reach the area, but only
formulas were picked, so a Python result blocked by a merged cell stayed
#SPILL! after the cells were unmerged; Python cells are picked too.