Uglify.js messing things up within if statement

I have this code

if (!win._hb_bids) {
    win._hb_bids = {};
}
win._hb_bids.hb_auction_id = helpers.generateCacheBuster();
if (config.isAmazon) {

translated with Uglify.js to this code

if ((p._hb_bids = p._hb_bids || {}) && (p._hb_bids.hb_auction_id = e.default.generateCacheBuster()), s.isAmazon)

I would assume that this code should be executed from left to right, setting _hb_bids property to an empty object. Instead, what I see in the Chrome debugger, generateCacheBuster() is executed first, and then it tries to make an assignment to p._hb_bids.hb_auction_id, and p._hb_bids is undefined at this moment.

What is the reason for such a strange execution order? And how the code can be rewritten to work correcly after uglify?

UPDATE: I found the cause of the issue. I had another part of the code doing iframe content refresh, and the win variable was pointing to an iframe window which was destroyed already. That probably caused this weird behaviour. So it wasn't uglify.js problem as I initially thought and stated in the title.