Maybe I'm missing something, but why there are exons that the start and end are the same?!

Examples: 



    1	havana	exon	2768091	2768091	.	+	.	gene_id "ENSG00000285945"; gene_version "1"; transcript_id "ENST00000648684"; transcript_version "1"; exon_number "1"; gene_name "AC242022.2"; gene_source "havana"; gene_biotype "lncRNA"; transcript_name "AC242022.2-201"; transcript_source "havana"; transcript_biotype "lncRNA"; exon_id "ENSE00003831437"; exon_version "1"; tag "basic";


    17	ensembl	exon	41624191	41624191	.	-	.	gene_id "ENSG00000128422"; gene_version "17"; transcript_id "ENST00000540235"; transcript_version "5"; exon_number "2"; gene_name "KRT17"; gene_source "ensembl_havana"; gene_biotype "protein_coding"; transcript_name "KRT17-205"; transcript_source "ensembl"; transcript_biotype "protein_coding"; exon_id "ENSE00003733771"; exon_version "1"; tag "basic"; transcript_support_level "5";


Thanks
Hmmm seems like an off-by-one error, as these exons are actually a single base long. But GTF is one-based so the coordinates indicate, indeed, a single nucleotide: https://www.biostars.org/p/84686/