490 is so far out of band, the PA is sucking up so much current to attempt to produce RF output, either the li-ion battery is dropping below 4.5V. Once the battery pack detects voltage below 4.5V, it shuts off the battery. If the li-ion battery is taken any lower than 4.5V, it may never take a charge again.
Li-ion batteries are sensitive to low voltage, as well as over voltage. Thats why there are lots of federal regulations on li-ion batteries. If li-ion batteries are over charged, they blow up with almost the force of C4. Thats why every li-ion battery must contain a regulation circuit for overvoltage & undervoltage detection.
Another thing that could cause the radio to freak out, is at 490mhz, your swr's are so high, there is very little power making it out the antenna. Most of the power generated by the PA, is being reflected back into the PA/Radio. This high level of RF inside the radio may be scrambleing up the CPU - causing undesired operation.