Hi fregas baratis,
When changing the type of a control property from string to string array, you should be able to see that property afterwards. Perhaps the disappearing is caused by something else or I am missing something here.
Clearing the invalid control properties is not an easy job for the time being. If you encounter any major issues with them, please let us know and we will send you a db script to clear the unnecessary information.
For the properties which have web editors, I can suggest two ways to achieve better usability.
The first one is to allow the field to be editable and create proper TypeConverter. The type converter is assigned to control via attribute. You could take a closer look at the attachment to see how you could implement type converter. This scenario is very useful for properties of array types as I think is your case. In the attachment you will find three files each containing a class for web control, type converter and web editor. The code is taken from the Lists module.
The second scenario is to create the property read only. This way the text box will not be editable and you could fill the property information from the web editor. This scenario is a bit complicated to implement and in case you need it, give us a sign and we'll provide you with the sample code.
All the best,
the Telerik team