Custom properties contents disappear upon reload of Visio document

I discovered this bug while creating a functional block diagram where shapes
representing electrical equipment are connected with Connectors.
Each Connector represents a Functional Channel with a unique ID.
I associated such ID to the graphic Connector by creating a Custom Property
Set with two properties: Channel ID (ChID) and Description.

I typed-in values for such custom properties, by using the Custom Properties
Window. In order to enter the typed value I used two strategies: either
pressing Enter key or clicking somewhere in the window.

By selecting the connectors with the custom properties already set, I could
see the correct value stored in each one. This as a confirmation that the
process worked.

Then I saved the Visio file, closed visio and re-opened the same file.

By clicking on the Connectors, I couldn't find any more the Custom
Properties values. The Custom Properties are visible in the Custom Properties
Window, but their value is blank (i.e. no value).

I have Visio 2003 Standard installed on the Dell D630 of my company.

Does someone have an idea about how to solve this problem?

I don't dare hoping to recover the data, but I'd need to use Custom
Properties intensively.

Thank you for reading all this stuff.

Bye.