Unfortunately the problem is real though due to latest changes to Chrome and the way the code in vbulletin generates text. See:
http://www.vbulletin.com/forum/foru.../4356452-space-bar-not-working-on-reply/page2 And a message from their support staff:
"Thu 27th Oct '16, 9:30am
Just to manage expectations - this is almost certainly an incompatibility between new versions of Chrome and the now quite old version of CKEditor that vBulletin 4 uses as its message editor.
There is no development work on vB4 now, as it is not the current product. The only work being done is php compatibility, any security issues that come up, and a handful of very minor bug fixes. Development work is focused on vB5.
Replacing the version of CKEditor in vB4 would be a major undertaking, requiring months of developer and QA time. I'm afraid that is not likely to happen.
Probably the best bet for any users affected is to get them to switch to the text-only editor ('source mode) instead of the WYSIWYG. They can do this in their user settings."
Hopefully the community will find a fix and or they change their mind and look into this.