After upgrading to version 5.0c I also ran into a problem. I have cards with 4 GB of VRAM, the worker has 4 GB of RAM and runs on Linux, and I mine Ethash on NiceHash. During the switching from ETC to ETH the miner process is killed by OOM killer. On version 4.9c this doesn't happen.
Smells like bug in 5.0C. Maybe PhoenixMiner should restart when switching the pools or coin and -dagrestart 1 is specified.