You are definitely doing an illegal short because you only liquidated your 1000 share long from your bullet leaving you 3000 shares shorted illegally. If discovered, there might be fines imposed by the SRO (NASD, NYSE, etc) Who gets the fine? That is a good question, some LLC's (actually I would think most of them would probably have stipulations in the agreement that the person responsible would eat the fine, trading losses. In my opinion, that is the biggest drawback of the LLc model. It has great benefits (capital usage, bullets,etc) but if the software somehow does'nt catch compliance violations and the violation happens daily and SRO fines per occurence.. it could get ugly. I guess you just have to hope that the software is good enough to prevent those compliance busting trades happen.