Are you then able to use the delete key?

If you highlight the text, then RIGHT click on the highlighted section, choose "Delete", does it then delete correctly?

If you haven't already, please try the steps below to scan your computer for malware.. Remove such if found.

On a friend or family member's computer, download the Malwarebytes installer and update files from the links below, copy them to a CD or flash drive, then transfer the files to the problem machine and use them. If you can't start the computer into "normal" windows, try installing, updating, and running the scans AFTER the computer is started into Safe Mode.. I use the sites below to download the installer file and the manual updater:

Once downloaded and before transferring them to the problem machine, rename the program installer "mbam-setup.exe" file to something else like "Gogetum.exe", then copy the installer file and the update file to a CD or flash drive.. Transfer the file to the problem machine, then install the "Gogetum.exe" file, then run the update to get the program current.. After that, run a full system scan and delete anything it finds.

Malwarebytes Installer Download Link (Clicking on the links below will immediately start the download dialogue window.)
http://www.besttechie.net/tools/mbam-setup.exe

Malwarebytes Manual Updater link
http://www.malwarebytes.org/mbam/database/mbam-rules.exe

Next, download the SuperAntispyware program and the manual updater from the links below. After running the Malwarebytes tool above, if you still can't download and install it directly from the problem machine, download it on a friend or family member's computer as well. After installing and updating SuperAntispyware, run another full system scan and delete everything it finds as well. As before, you may need to rename the installer file to get the program to install.:

SuperAntispyware
http://www.superantispyware.com/

SuperAntispyware Manual Updater
http://www.superantispyware.com/definitions.html
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In a few situations, in order for the program to run, it was also necessary to rename the main "mbam.exe" file also after installing it.. It resides in the C:\Programs Files\Malwarebytes Antimalware folder.

Hope this helps.

Grif