There is no inherent reason a Spektrum RX should flash simply because it was turned off and on with the TX remaining on. You're presenting absolutely nothing to the RX in that condition that you don't ALWAYS present it with during a normal startup.
Ok lets get this straight.
Turn on the transmitter and it searches for two open channels and locks on. It then begins transmitting its GUID on those channels and waits for a response from the reciever its bound to.
Turn on the reciever. Here's where it gets a bit tricky.
IF the receiver has the oldest firmware it searches the band for the transmitters GUID, once it finds the GUID it locks and and the lights come on steady. This takes 3 to 5 seconds.
If you loose power in flight it goes through this link up sequence.
IF the reciever has the newer firmware, the reciever has a buffer with the last two channels in use and checks those first. If it finds it's transmitter there it links instantly and the lights come on steady.
IF it has the LATEST firmware, it checks the buffer channels, locks on instantly, and flashes the lights.
If it has either of the two newer firmware versions and does NOT see the transmitter GUID on the last two channels it used it searches the band, finds the GUID, and locks on in 3 to 5 seconds and displays solid lights.
The key is the last two channels in use. If you power cycle the transmitter it automatically searches for two new channels. THAT is the difference in what you're presenting to the reciever during a normal turn on sequence, or if you turn off power to the reciever without turning off the transmitter.
The flashing lights with the new firmware are designed to tell you when you suffered a low voltage condition during flight, it has nothing to do with signal strength.