I don't think the interface is very intuitive. When you click on 'Restore Full Delivery' for your first time you say to yourself, "nothing happened?!?!" so you click it a few more times, and then a few more. Then you try a different page in your account and it's still there. That's usually when you try a log out. I don't recall this requirement being stated in the text box near the restore button and it's not in G's email that they send you, relevant text below:
Once you have refined your under-performing keywords and optimized your
ad text, you can restore full delivery to your campaign. Simply press
the 'Restore Full Delivery' button at the top of the 'Campaign
Management' screen in your account. Please note that if your campaigns
continue to perform below the minimum required CTR, we may ask you to
optimize your campaign further.
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* This keyword has been disabled because its clickthrough rate (CTR) for the last 1,000 ad impressions it generated on Google falls below the minimum required CTR.
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I know they keyword in question and read the archor link to the google faq page on this issue, but it doesn't say whether the keyword would be allowed to be used.
Can disable keywords be used again?
I got a red asterisk for a keyword shown just 1 time!
Google says the minimum CTR is calculated upon 1000 impressions, so what about the other 999?
I'd bet dollars to doughnuts (I have just been waiting for a chance to say that!) that you haven't deleted the disabled keyword every place in which it occurs in your entire account - even in other campaigns.
If you don't delete it everywhere, then re-use the keyword, it will be disabled immediately. Why? Well, because it still disabled from its previous use.