The attached macro creates two TH2F histograms, one has 3 bins with content 1.5 while the other has the same three bins filled with 1.5 in two cases and -1.5 in one case.
When drawing them with the BOX option, the histogram with no negative bins draws as expected, while for the other all the zero-entry bins now have boxes drawn.
I have tried a few ROOT versions and the problem is present in 5.34.28 and 6.06.06 but the plotting works as expected (i.e. the histograms appear the same except for the cross in the single negative bin) in 5.33.02. So it seems to have come in during the 5.34 series. I wonder if it might be related to whatever was done to fix