The ZX14 and C14 should behave exactly the same if the config and bulbs are actually the same. So I would assume that either the resistors they provided were defective or under-speced, or maybe you installed them incorrectly- perhaps on the full-time-power wires instead of the turn wires?
If one replaces only the front lamps with LED bulbs, there might be enough load in the rear incandescent bulbs to still flash correctly- but perhaps faster than normal (since it was designed to see 42W/84W of load (turn/hazard)). There is no chance of avoiding "hyperflash" with LED bulbs in all 4 corners without the use of load resistors or a replacement flasher unit.
The ZX14 and the C14 SHOULD have behaved the same. They did not. We were using turn signals that had built in resistors. Everything was from the same manufacturer, the ZX just didn't like it.
The Auxito LED turn signals that I linked to at the beginning are the ones with the built in resistors. They did not hyperflash on my C14 or anyone else that I know who got them. The ZX is the only one.
When I added in the new sockets and bulbs, the turn signal was the only thing even hooked up when I had the ballast resistor in-line. I hadn't even connected the key on power yet. It's probably due to the rear bulbs still being LED. It wasn't unexpected, that's why I tried it out before finishing the install.
I could ohm out the resistors that the kit came with, or do the same with my flasher circuit, but neither is needed. This isn't about somewhat expected hyperflashing. I don't know that I'm even going to correct it.