We could reproduce that the keyboard is removed, but this is totally normal. If the page is loading still, then it will remove the keyboard to load the page.
We can reproduce that and also reproduce it on Safari.
If it's something we are missing, then i would say it would be great if you could just open a ticket so we can look into it deeper. Even with a video would be awesome.
Here is the link to it: https://issues.adblockplus.org/