I do not understand overlays very well, but it looks like verilog-mode or some minor mode created 5 overlays over the same region, and they did not get removed even when those modes were disabled.
Some more info.. with each revert-buffer call, that overlay is replicating over the same region.. I reverted the buffer 4-5 times and now in the C-u C-x = generated Help buffer, I see..
From 1466 to 1482
end-closed t
evaporate t
local-map [Show]
mouse-face highlight
start-closed t
verilog-include-file t
From 1466 to 1482
end-closed t
evaporate t
local-map [Show]
mouse-face highlight
start-closed t
verilog-include-file t
...
(and so on 27 times!)