cant whisper because i didnt write a big lether

i have some issue where i have never seen it before and idk how i got it so look. when i whisper /w "name" it just says that guy isnt online but when i /w "Name" i can normaly whisper it bothers me really much because when i look in global chat and i find raid room i cant whisper guy if i type thatguy but i have to type Thatguy and i always miss to use my caps ......... so if anyone know how to fix this please tell

I have never experienced this issue, it shouldn't matter whether you write lowercase letter or uppercase.

However, to go around this issue (safe to say a bug, if what you say is true), avoid typing "/whisper name" at all. If you want to whisper a dude from global, left click on his nickname and whisper window will appear. Same applies to anything you see in chat.