is there a reason for this abnormality, or even a way to conclude what key was pressed and then I can evaluate the text on my own?

Because its drawn that way :)

See https://metacpan.org/source/SREZIC/Tk-804.033/pTk/mTk/generic/tkText.c

See https://metacpan.org/source/SREZIC/Tk-804.033/Text/Text.pm

 $mw->bind($class,'<Delete>','Delete');
 $mw->bind($class,'<BackSpace>','Backspace');
[download]

This corresponds to sub Delete and sub Backspace which just calls delete