Attach (recommended) or Link to PDF file here:
[example.pdf](https://github.com/mozilla/pdf.js/files/6916129/example.pdf)

Configuration:
- Web browser and its version: Chrome, Firefox
- Operating system and its version: all
- PDF.js version: various versions, including 2.11.54
- Is a browser extension: no

Screenshot with visible textLayer:
![Screenshot from 2021-08-02 13-05-03](https://user-images.githubusercontent.com/6362989/127844878-f85e291f-2060-4028-be09-7835f32ccfaa.png)

Which means some letters at the beginning/end of text selection are missing when copying text.

? `${elf.dFactry.getPageObjId()}_mcd${mcd}`
                  : null,
                tag: Name(arg[0]) ? arg[0].name : null,
              });
            }
            break;
          cae OPS.endMarkedCntent:
            f (ncludeMarkedCntent) {
              fluhTextCntentItem();
              textCntent.tem.puh({
                type: "endMarkedCntent",
              });
            }
            break;
        } 
        f (textCntent.tem.length >= nk.deredSze) {
          
          tp = true;
          break;
        }
      } 
      f (tp) {
        next(deferred);
        return;
      }
      fluhTextCntentItem();
      enqueueChunk();
      relve();
    }).catch(rean => {
      f (rean ntancef AbrtExceptn) {