Yes it will. The shares are borrowed from source A. Source A calls back shares upon assignment and moves shares to Source B (Icahn's broker). Ackman borrowed from A not B. The buyback cant be avoided provided the broker is different. Oh maybe he can borrow some shares from Icahn to continue shorting HLF. And you know what? I think icahn might even lend it to him so he can time further squeezes even better.