Eclipse could be remembering the size of the dialog for content assist UI in the workspace/.metadata directory.
Try editing this file: <workspace_dir>/.metadata/.plugins/org.eclipse.jdt.ui/dialog_settings.xml
Look for the section that looks like this:
<section name="completion_proposal_size">
</section>
In my workspace there is no special settings here, but perhaps there are some special settings in your workspace.
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solved Eclipse autocomplete view became wide and block the whole screen [closed]