I don't think it's a case of the synchros going bad. Actually, I'm pretty sure they don't even come into play when the transmission and the engine aren't both turning. That's why most older cars didn't even have synchronizers for 1st & reverse - you only shifted into those gears from a standstill. I've driven sticks for 30 years, and have experienced this problem on many cars.

Either way, the 'second to first' or second to reverse' move should take care of it.