So kind of confusing, but when I drink a Witch's Brew, it raises all my stats similar to a super set. Whenever the pot starts to wear off and I drink another sip, it refreshes my attack and defense, but not the strength.

For example, my base stats are:
89 Attack
76 Def
99 Str

Half potted through witches brew:
Currently at:
102 Att
87 Def
111 Str

When I re-sip the pot:
107 Att
92 Def
111 Str

It seems only the strength will not refresh. I have tried dying, drinking super restores thinking it is bugged with a curse. If I do the same with a super strength it does refresh my str back to 118.