IOTA updating metadata but not the value

It seems that under some circumstances (we have asked for more information) upon receiving a measure the IOTA is updating attribute metadata of entities not belonging to that measure, but without updating the attribute itself.

For instance: we have and entity with attributes A, B, C, D in CB this way:

• A=1, TimeInstant = 10:10
• B=2, TimeInstant = 10:10
• C=3, TimeInstant = 10:10
• D=4, TimeInstant = 10:10

IOTA receives the following (UL) at 10:30 in the device associated to that entity:

C|30|D|4

The entity now is:

• A=1, TimeInstant = 10:30
• B=2, TimeInstant = 10:30
• C=30, TimeInstant = 10:30
• D=40, TimeInstant = 10:30

The weird thing is that IOTA doesn't know the values or A and B (the didn't come in the measure) and, as far as I remember, there is no operation in CB that allows updating metadata without specifying also the attribute value in the same request.

To be analyzed.

Start by tracing how an incoming UL measure is parsed and how the resulting update is sent to the Context Broker. Reproduce the C|30|D|4 example, compare the generated request with the attributes updated in the broker, and document the cause of metadata changes for attributes absent from the measure.