You guys really mucked up the implementation of the extranonce subscription extension. Of all the ways you could have done it, you chose the only option with the potential to create enabled mining clients that are incompatible with other pools by default. You had full control of your stratum server implementation, and full access to nearly all client miner implementations, but little or no access to oftentimes proprietary stratum implementations at other pools, so the fact that you decided to initiate extranonce subscription messages from the mining client side, demonstrates either your incompetence or ignorance as to how to extend an already well established protocol without introducing negative consequences elsewhere, or callous disregard for the effects upon miners and the other pool operators who are affected by your protocol extension.
Given the circumstances, you should be initiating the extranonce subscription from the stratum server side, at which point an enabled mining client can respond in the appropriate fashion, and an earlier version ignore the message as you can easily verify that most mining clients do. But as it stands now, you have created a situation where extranonce subscription enabled mining clients are sending unexpected messages to stratum servers at other pools potentially causing unknown consequences there. Or was sabotaging your competitors part of the original plan?
I have to agree with this (except the last sentance, which is kinda stupid).. I wonder if it is already too late to change this (also, this is just a feature nicehash added, or is it some standard?). I did not go into what this is actually useful for, if it's only for these rental/multipools, then we could simply turn this option off by default (opt-in instead of opt-out).
Please do open github issues. I think most of the developers (including me), are not on forums that much, compared to github where we will see the issue very fast and can respond much faster. I guarantee you, things will be fixed faster if you open an issue for it, and especially do that if multiple people are having the same problem.
For anyone who doesn't know, issues can be reported here:
https://github.com/sgminer-dev/sgminer/issues (please mention if you are using the v5_0 version)
