The most common symptom, when reported, is very simple.
Once we explore the problem itself, we see various possible causes.
The base cause for problems with the HTML / Text gadget is simple - the script which processes gadget updates provides no diagnostics when detecting errors.
If you update a post (using Post Editor), or the template (using Template Editor), with bad code, you generally see some error message, indicating that your changes are bad.
Both Post Editor and Template Editor provide some diagnostics, when errors are detected. With the HTML / Text Gadget, the script issues no error messages, it simply stops.
- Bad HTML, when accidentally in HTML mode.
- Bad HTML code, when intentionally entering an HTML gadget.
- Gadgets with blank titles.
- Layered security, which blocks the gadget update scripts from running.
- Trying to use a non supported browser version.
- Changes to the blog or post template, unwisely applied by the blog owner.
- Using the wrong menu selection, in "Add a Gadget".
Blog owners who are not observant, when updating the gadget, may accidentally be in HTML mode. Rich text, containing HTML significant characters, will be a problem.
Gadgets with blank titles will cause a problem, when using some browsers. If a gadget with a blank title is specifically required, it may be possible to use a null title, instead.
Inappropriate use of layered security may block cookies or scripts, and prevent the gadget from updating. This can include browser add-ons, as well as security applications. The owner may intentionally cause this problem - or this can be entirely without owner involvement.
The gadget, like every other Blogger feature, must be updated to support newer browser versions. It will likewise be updated periodically, to remove support for older browser versions. Non supported browser versions will frequently cause problems.
Blog owners can make unwise changes to the blog or post template, which can interfere with gadget code, elsewhere in the template.
Some of these error scenarios should be more clearly identified, by the script - but not all can be identified. Attempting to save a gadget with a blank title, for instance, should produce a stern warning
Blank titles are not accepted.Unfortunately, HTML syntax errors generally can't be consistently diagnosed, with any detail.
The best solution here is for the blog owners to be aware that the gadget operates this way, when being updated. Some cautious effort must be made, when updating the gadget.
It's possible that problems updating the gadget, like many Blogger problems in general, can be best diagnosed using affinity testing, and / or differential testing.