WorkListMode values and worklist behaviour

I am using Conquest DICOM 1.4.17, and PostgreSQL 8.4 as backend. Worklist has been enabled by setting WorkListMode to 1.

Conquest manual indicates that WorkListMode allows to choose between the following worklist behaviours:
- WorkListMode=0: (default) Disabled
- WorkListMode=1: The AccessionNumber is looked up in the local WorkList database, if it is found, any element in the DICOM object that is also present (and non-NULL) in the WorkList database, will be replaced by the value from the WorkList database. These changes are made both in the database and in the image that is stored on disk.
- WorkListMode=2: As mode 1, but the image will be refused if the AccessionNumber is not found. Note that there is no DICOM method of filling the worklist database. Use drag and drop to enter HL7 files into the server. Conquest addition since version 1.4.9.

Recently I have detected that when a study is transferred to the server from a modality, the attribute "modality" (0008,0060) in every series is changed to the value of the corresponding worklist item (the one with the same AccesionNumber). This is a problem because many studies include series of captured images (SC); and there are also studies including series of different modalities (PET and CT, NM and CT, ...).

This problem appears when a study is archived while corresponding worklist items are not removed from worklist. This is a very common situation, because modalities usually transfer images to Conquest right after acquiring them.

I have tried to set modality attribute to null on every worklist item, but then an error is detected when a modality refreshes worklist.

Is there any way to prevent this undesired modification of series modality attribute?

Thank you, Marcel, for your prompt answer.

I have tried to set it to null but then equipment operators report an error that pops up when they refresh worklist. The error indicates that modality field (0008,0060) is missing, and worklist record is considered incomplete.

Is there any other way to fill in modality field so that clients receive a complete worklist record, but Conquest ignores it at the moment of archiving?

Is there any way of keeping worklist activated and disabling data replacement when a study is archived?

IT worked perfectly. Thank you.