When I lift this region: chr1 145686997 145808272 from hg38 to hg19 on UCSC browser I get: chr1 145626811 145748066. However if I do the same with rtracklayer (R package) I get a bunch of fragment overlaps, and if I take min of start and max of end it corresponds to: chr1 145626812 145748067

Why is it slightly different? Also, is there a simple way to obtain a 1-to-1 mapping as in UCSC instead of the several fragment overlaps using this tool? I'm not sure if min and max is the clean way.