Network adapter driver can't get any signal when network manager request 'disconnect'

[howwow20]

I'am developing a wireless USB data modem(3G, LTE).

USB Network adapter driver can't get any signal when network manager request 'disconnect'.(that means click disconnect in Network Manger).

Also, I checked belows after Network Manager request 'disconnect'.
1. ifconfig <name> -> Status is RUNNING
2. ethtool <name> -> Link detected: yes
3. /sys/class/net/ptuml290/carrier value is 1(link on)

I think that Connection is not actually disconnected. Because RUNNING is not appared, yes -> no, 1 -> 0 when connection is disconnected.
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1. Why doesn't USB Network Adapter get any signal when network manager request 'disconnect'?
Driver need a signal to process 'disconnect request'.
Is it normal? I think that this issue is because of ubuntu(actually Network Manger).
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And after Network Manger request 'disconnect', Connection Manager's status is 'Connect-dormant'.
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2. Is there any way for Connection Manager's status to change from 'Connect-dormant' to 'disconnected' ?
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Thanks in advance.