Steps to reproduce the issue

Create an article or custom module with some text containing two spans, one without a class and another with, e.g:

<div>This is some text. <span>This part has a span tag</span> and this doesn't.</div>
<div>This is some additional text. <span class="span">This part also has a span tag</span> and this doesn't.</div>

Save
Tinymce will revert back to the main editor
Toggle back to the code view

Expected result

<div>This is some text. <span>This part has a span tag</span> and this doesn't.</div>
<div>This is some additional text. <span class="span">This part also has a span tag</span> and this doesn't.</div>

Actual result

<div>This is some text. This part has a span tag and this doesn't.</div>
<div>This is some additional text. <span class="span">This part also has a span tag</span> and this doesn't.</div>

System information (as much as possible)

J4.1.0 but I first noticed it yesterday with J.4.0.6

Additional comments

This does not happen with JCE Editor