I've seen a few posts that seem to be related to the same bug I'm trying to get around. It's getting cold up her in Northern Maine, and today I replaced a PC with a IDE flash module running Mikrotik with an RB532/A with 6-port daughtercard.
When I boot the unit with an APC SmartUPS 1500VA attached to COM1, the RB532/A refuses to boot. When I disconnect the serial cable and power-cycle the board, it boots fine. Then I attach the serial cable, and the RB532/A starts talking to the battery with no issues.
I couldn't leave the battery attached to the RB532/A, because after a power outage I would have to travel to the tower site to disconnect the serial connection. This leaves me with no remote battery monitoring.
Under system/console, I have deleted the console interface. Under ports, COM1 is shown in use by "UPS". When connected, system/UPS shows data from the battery.
I suspect what is happening is that on boot, the RB532/A is receiving data from the battery through the serial port and doesn't know what to do with it, so it locks up.
Does anyone else out there have the same problem? Is there a fix or a workaround? It almost seems like this needs to be solved in the RB532 hardware.