I've been having a problem in Evernote on Windows 10 where font size decreases the first time I hit to create a new checklist item. After some forum searching and back-and-forth with the helpful support folks at Evernote Support, I found two workarounds:

Just wanted to share this in case it's helpful for someone else.

To further describe the original problem, here are steps to reproduce it:

1) Using Evernote for Windows, create a new note

2) On the first line, click the checkbox icon to create a to-do item, and type some text

3) Hit Enter key to create a new to-do item

4) Start typing; note that the font size went down

5) Select text in the new line and note the font size displayed in the font-size drop-down

6) Select text in the first line and note the font size -- it's reportedly the same as the second line, even though they are clearly different

Another way to see if you're having this problem is to set your default note font size to 10, then create a new note. If the size shown in the font-size drop-down in the toolbar is 9, you'll also run into issues where the font size of new text suddenly becomes smaller.

Thanks to Kimball on this forum thread for finding the causal factor behind this bug!