Despite the fact that Yola denies this is a problem and it doesn't occur I can guarantee that it does.

There are a couple of aspects of this:

Misstyped ' or " in a Tag will be added as typed  and will be displayed in the Tag list. Similarly non-Roman Characters  will be added and displayed. An expample would be the +, the - and the / characters. They cannot be searched for.

Subsequently doing a search on Tags containing these characters will not produce a result. The displayed results will simply state there are no Tags with "". It seems as if the accepted characters are invalid within the ability of the Yola blog recovery process. This is not highlighted in any note or instruction anywhere. In fact Yola state that it is not a problem and that these can be recovered as any normal Tag.

These characters until recently were valid.

The next issue is removing these characters. You have to go through each record one by one to find these invalid tags, and manually remove them. Quite a tedious process for 600 or more records.