UserAgent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:45.0) Gecko/20100101 Firefox/45.0

Steps to reproduce the problem:
1. Open the following sample https://jsfiddle.net/3gqghyr5/1/ OR attached html file
2. Click the "start" button
3. The select drop-down will open and the field will move to the left as soon as the new content is added

What is the expected behavior?
The opened menu should move with the field as well

What went wrong?
The menu displacement appears

Did this work before? N/A 

Chrome version: 49.0.2623.87 (32 bit)  Channel: n/a
OS Version: 6.1 (Windows 7, Windows Server 2008 R2)
Flash Version: Shockwave Flash 20.0 r0

Attached the sample as HTML page as well
 

Deleted: select-menu-displacement.html 3.2 KB

select-menu-displacement.html 3.2 KB View Download