In the following example, say I had a majority of stake at block A. Then at B0, C0 all the way up to head block H0, I sell off my majority of stake, understanding that there is an upper limit on stake transfer.
A - B0 - C0 - D0 - H0
\ B1 - C1 - D1 - H1
Then, I create a double spend of my stake using the historical private keys, which I still own, thus sending it to myself in a fork continuing fork B1 - C1 - D1 that I create and approve myself (majority stakeholder).
Indeed, interesting, very valid point. I suppose you mean the security rule named "validator's bond" or "security deposit", so that after "depositing" (required to become a validator) some amount of tokens, it is not possible to "withdraw" immediately. It is not mentioned in the document, but should be easy to add in order to address the issue you mentioned.