Reason is that the wiki markup looks like that:
See also:[[Calc/Spreadsheet_Functions|VLOOKUP]] (columns and rows are exchanged)
as the link is on the same page, the linktext simply gets boldface. It would work if [[Calc/Spreadsheet_Functions#VLOOKUP|VLOOKUP]] or [[#VLOOKUP|VLOOKUP]] would look like.
Gabor Kelemen committed a patch related to this issue.
It has been pushed to "master":
tdf#97821 Add section anchors to VLOOKUP/HLOOKUP links