How To Avoid Double Posting During These Changing Times For The Steemit Platform
As you already know, Steemit is rolling out some updates these days, including a new backend. As with any change, some things are not always going as planned, so there are a few glitches.
The most important one is related to posting. The error checking got a bit aggressive in this version (which I like) but it kinda trespassed into the other side, reporting errors when there aren't really any.
So, my suggestion to avoid double (or triple, or quadruple) posting is to check if the post really has been published, just after you hit "Post" (wait a few seconds) in a different tab.
So, ideally, you should have two open tabs on Steemit all the time: one for posting / commenting, and the other one for checking if the post really went through. Even if you get an error like: Type error: RPC timeout, or Type error: Network timeout it doesn't mean it really is an error. Just check if the post was actually pushed to the blockchain, and if it was, come back to the first tab and click "Clear" to empty the form.
It's a little bit cumbersome, I know, but tough times require tough measures. I will try to let you know when this behavior disappeared completely, but I guess it will take a while.
Steem on!
I'm a serial entrepreneur, blogger and ultrarunner. You can find me mainly on my blog at Dragos Roua where I write about productivity, business, relationships and running. Here on Steemit you may stay updated by following me 
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If you're new to Steemit, you may find these articles relevant (that's also part of my witness activity to support new members of the platform):