HI, Paul.
Thanks for the question and I believe I know what is happening. I understand that the Finder or Spotlight search options appear when you hit the Space bar. This actually sounds like a keyboard shortcut may be activated when typing. If you select Command–Option–Space bar, the Finder window will pop up. If you select Command–Space bar, the Spotlight Search option will appear.
Mac keyboard shortcuts
You can disable these shortcuts by opening System Preferences, click Keyboard and then click Shortcuts. Once there you need to select Spotlight on the left, then deselect the checkboxes for "Show Spotlight search" and "Show Finder search window."
OS X El Capitan: If Spotlight or the Finder opens when you switch input sources
If you are still experiencing this issue, try going through the steps in the article below. You may also want to look for any stuck or depressed keys when looking at the keyboard viewer.
If other keys don’t work
You may have accidentally set an option that changes how your keyboard operates.
Choose Apple menu > System Preferences, click Dictation & Speech, then click Text to Speech. If “Speak selected text when the key is pressed” is selected, deselect it or click Change Key to select another key.
Choose Apple menu > System Preferences, click Accessibility, then click Keyboard. Make sure Slow Keys is turned off. If Slow Keys is on, you must hold down a key longer than usual before it’s recognized.
Choose Apple menu > System Preferences, click Accessibility, then click Mouse & Trackpad. Make sure Mouse Keys is off. If Mouse Keys is on, pressing keys in the numeric keypad moves the pointer instead of entering numbers.
Choose Apple menu > System Preferences, click Keyboard, then click Input Sources. Select “Show Input menu in menu bar.” Open the Input menu, then make sure the correct keyboard layout is selected.
To see the keyboard layout, click Keyboard, then choose “Show Keyboard, Emoji, & Symbols Viewers in menu bar.”
OS X El Capitan: If keys on your keyboard don’t work
I hope this resolves your issue and thank you for visiting Apple Support Communities.
Cheers