Dont know if anyone has had experience of this strange set of events…
It started with an export that appeared to fail - clicked the export solution button and nothing happened. Tried this twice, then restarted and tried again - this time all went as expected.
BUT having imported the solution to the server, strange things began to happen - type ahead fields using a valuelist failed to return a selected value. Went back to the developer version and the same field was actually returning a value that was not even in the valuelist! - the value being returned was a table name followed by a number whereas the valuelist only actually contained a list a simple text items.
So I deleted the value list and replaced it with a new one of the same name - same problem recurred! Finally I created a new valuelist instead and the problem has gone - now the field returns the selected value from the valuelist.
Looks to me as if the valuelist itself had become corrupt - I cannot find any other explanation But I’d love to hear another explanation!