In my opinien are inputfields not a stable solution for the long-term without doing some kind of backups - exports to flat-files and loading them again regulary or if it's necessary - maybe other solution like SQL Writeback from QlikView extension object. are more suitable.
AFAIK inputfield-values are stored with the shared-files. Therefore it might be useful to make regular backups from them and using from the shared-file viewer from the power-tools: PowerTools 1.1 for QlikView.
The reset from the values is probably mostly caused by changes within the data-structure - if new dimension-values are loaded or the load-order changed and likely some more reasons.