On my previous question, I received an answer telling me that the reason 't' in "Winter" didn't shift to 'z' is because of the following 'r', that High German Consonant Shift didn't apply to 't' followed by 'r'. And that the same is true for the word "bitter".
However, I can't help but notice that sometimes High German Consonant Shift did apply to 't' followed by 'r'. Consider the English word "better" and its German cognate "besser". So, what's going on there?
In Proto-(West)-Germanic there was still a vowel between the *t and *r in the antecedent of better, *batiʀō, whereas the antecedent of bitter, *bit(t)r had no such vowel separating the *t and *r. Note also that the antecedent of bitter has a geminate already in all the Old Germanic languages (although in Old English it does appear alongside an ungeminated form), and this may also have provided additional protection (this complication is why I did not use it as an example in my answer linked in the question).
As such the *t in the antecedent of better was just a perfectly normal intervocalic *t and followed the High German Consonant Shift, where the *t in the antecedent of bitter was protected by the following *r.
