This is a well known effect for those who experiment with using the pipe character (|) in title tag. I mention it here in an update: Pipes or colons in HTML title tags? which I should update again with new findings when I sort out my thoughts.
When the pipe character is used in a title tag, Google treats the tag as a keyword list. This does not work for other characters- it is a relatively new effect following a trend. If the domain name, either with or without the TLD, appears at the end of the list Google takes it as a branding signal and will place
example.com : at the beginning of the title tag and remove the keyword from the end of the title tag.
For example: a title tag of
cakes | chocolate | bunt | example should appear as
example.com: cakes | chocolate | bunt. This works with or without the TLD if the last keyword matches the domain name.
If this is not what you want, you should remove your branding signal from the end of the list.
Branding a title tag is a good idea, but must be managed. If the title tag is short enough but not too short or weak in Google's eyes, Google will automatically brand your SERP link with your domain name with
- example.com at the end of the SERP link. I made use of this effect for quite a while. Google feels that branding is a strong signal for improving click-through rates (CTR) in the SERP listing. And they are right.
But I can understand not wanting branding. I recently dropped my branding signals for the SERP list but cannot tell you there is a difference. I recently switched to using pipes for specific keywords and this works a charm. While I do not always recommend keyword loading title tags, recommending to choosing only 2-3 keywords at the most, if it is important to use keywords for competition, then I recommend using pipes. But this is limited to only signalling keywords, not for search so much, as market signals- What sites should you be compared to? For example, the keywords I used have nothing to do with returning users since these are not keywords that they use to find my site, but signal rather what market my site fits into.
For example, a
title tag can be
How to bake a German Chocolate Cake and the
h1 tag and
description meta-tag supports the title tag appropriately and are perfectly weighted and written. You will get searches for
how to bake a german chocolate cake. But let's say you change the
title tag to
recipe | german | chocolate | cake | food | cooking, you will see that
german, chocolate, cake will result in the same search results, but
recipe, food, cooking will signal the market your site is in and may push your results up higher in the SERPs as a result. It is a result of semantics more than anything.