Please always post complete documents, not just fragments, if you had added \documentclass{article} to your code and tested it you would have seen that it generated errors:
! Extra alignment tab has been changed to \cr.(twice)
Once that is fixed, the remaining problem is really a failure in acrobat, xpdf does better as may be seen on the left here:
You can however make it easier for acrobat by drawing the rule on top of the grey panel:
\textit{111.1}\\ \multicolumn{14}{|>{\columncolor[gray]{.8}}c|}{\textbf{$A\times{}B\pm{}C$} Program} \\\noalign{\vskip-12pt}\hline \noalign{\vskip12pt}\hline\textbf{111 of 111} & acrobat then does better:
