In IE, if you click in the middle of a word and while press-and-hold Shift key click somewhere else within the same word boundary, it would select the letters from the first click till the last click.
Like in word "Microsoft", if your first click was between 'c' and 'r' and second click (while holding Shift key) between 'f' and 't', it would highlight 'rosof'.
Now, if the second click is performed beyond the current word boundary, it will move the location of first click to at the start of the word boundary (or at the end, if second click is performed backward) and also move the location of second click to the end of the word (in case the click took place somewhere in between the word).
For example, in the sentence "Microsoft is a software giant.", if your first click was between 'c' and 'r' of word "Microsoft" and second click (while holding Shift key) was performed after the letter 'g' of the word "giant", it would highlight 'Microsoft is a software giant' instead of 'rosoft is a software g'
Please provide an option similar to the one Microsoft word has "When selecting, automatically select entire word" under File > Options > Advanced: Editing options. Deselecting this option should precisely pinpoint the selection where user clicked.