[TxMt] convert tabs to spaces

[Sean Allen]

i've noticed an interesting phenomena where i run convert tabs to  
spaces on an entire buffer,
go to a line that had tabs, hit the delete button and it sometimes  
takes me back a full tab stop
seemingly indicating the the conversion of tabs to spaces wasn't done.

would this be the case or is there some trickery involved that just  
makes it look that way?