Good find, but there is a difference between convertible bonds with a buyback clause (where the buyback conditions are explicitly described in the bond contract). Certain corporate bonds have conditions where the issuer can buy back on the secondary market, but I don't see TBP as one of these bonds as it is described in the contract.
There were a lot of things missing from the PPT contracts. It's not clear what we should assume to fill in the gaps in many places. Since this is win/win though, I can't see any sensible reason to prohibit it. (And that's not typical. Normally, you can buy your own debt. So far as I know, there's no prohibition on insider trading that would cover this absent actual inside information.)