Your item or field names must be including non-alphanumeric characters other than underscore, caret or dot in order to raise the issue; we clarified the constraints
here.
In fact, Html Client Library version 5.0 build 1443.3 introduced a strict check on the characters used for item and field names and would even replace unacceptable names with placeholders, as you have noticed.
Admittedly, this was annoying.
That's why, in the Html Client Library version 5.0 build 1443.6 we have rolled-back this check. You can download this version as part of the recent patch release.
Actually, as item and field names can be used in you html code directly, we decided to include few special characters among the ones allowed, but you can use other characters if you guarantee that there are no interoperability issues with your html code; the new library will accept them.
With the next major upgrade of the Html Client Library we will fix the issue for good.
