Actually here are better instructions 

1. Launch chrome here http://www.w3schools.com/tags/tryit.asp?filename=tryhtml_select
2. Bring up JAWS17 on win7
3. Tab to select and hit enter key => select dropdown expands
4. Arrow down and select any option and arrow down out of select
5. Arrow back to the select and hit enter key => Notice, inline choice dropdown does not expand
6. Hit enter key 2nd time => Notice, select dropdown expands

I don't seem to be able to reproduce this.
When you say that I have to cursor out of the combo box, how should I do that?
After expanding the combo box and moving up / down with the cursors, I tried pressing enter to select an option, then moved to another part of the page using the virtual cursor and then returned to the combo box. Only one press of enter was required to expand the combo box a second time.

I mentioned this on the call, but its really only going to apparent what's going on if you can see the screen.

Issue has not been modified or commented on in the last 365 days, please re-open or file a new bug if this is still an issue.

For more details visit https://www.chromium.org/issue-tracking/autotriage - Your friendly Sheriffbot

Clicking the selected option via |DoDefaultAction| should close the combo box. We should investigate is Jaws sends the enter key through, or if it clicks the selected option when a user tries to get out of the combo box and return to virtual cursor mode using enter.

My simple steps, since tab does not make it past the editor in the sample page:
1. Load page
2. Press Shift+tab. This should land you on the combo box
3. Press Enter. Nothing happens
4. Press Enter again. Combo box opens.

Notes:
- Enter never opens the combo box in Firefox, with or without JAWS
- Enter opens the combobox correctly, the first time, in Chrome without JAWS
- Spacebar opens the combobox in either browser
- The bug does not occur in a page with just a <select> in it
- It is easy to cause the bug to not occur, but I'm not 100% clear on what makes the difference

This bug does not occur if alternate user directory mode (Insert+Space Z). Turning that mode back off (same key) and force-reloading the page (Ctrl+F5) makes it occur again.

This is related to JAWS verbosity level -- it only happens when verbosity is high. FS working on it.