Safari: Space bar drag moves cursor to previous position

I was working regarding website prompts on Safari.[1] But as soon as I tap and hold the space bar while I'm entering a prompt, and drag it to move the cursor, it moves to the position that I moved to before. Why does it do that? Can apple's developers fix this?

[1] I'm sorry. But I am almost fluent in English but don't know what 'regarding' means. Can Apple's moderator fix this to an actual meaning?