Hey man.
First, check in the MTA>Settings section and make sure you reset the settings. Then log into the MTA and try again.
Also you can try to fix it by your mouse settings.
To fix:
1. Search for 'mouse', click Settings, then 'Mouse' with the mouse icon.
2. Click Device Options.
3. Click Settings.
4. Expand the 'Pointing' category.
5. Click PalmCheck, then the little cog icon next to it.
6. Put the slider to Minimum or Off.
7. Apply, OK, and you are done!