Immediately after the release of Opera 12, many people discovered this bug in the x64 version:


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By turning off the css-properties in Dragonfly one can understand that this effect has a non-zero letter-spacing value.
Accordingly, temporarily you can solve the problem like this:
*{letter-spacing: 0 !important;}
A file with this line should be added to Settings »Advanced» Content »Customize Styles» User style file, and do not forget to remove it after the release of the bugfix.