new joystick works not right with MAVProxy SITL

when I follow the [tutorial](https://github.com/ArduPilot/MAVProxy/blob/037ca9570a42ac22660e53a89709045171ac40cc/docs/JOYSTICKS.md) to add a new joystick, my computer can detect eight channels, but after I create the yml file to begin a SITL with mavproxy, it can still detect my joystick, but the fifth channel and the seventh channel cannot be detected correctly. When I flip channel 5 on the radio, the RC Channel 5 has no response at all. When I flip channel 6 on the radio, the RC Channel 7 and RC Channel 8 change at the same time. Simultaneously, when I flip the channel 8 on the radio, the RC Channel 8 has no response.

I use the last version mavproxy. and I use the futaba T16IZ joystick and a wireless dongle. It's a multi-in-one [wireless dongle](https://item.taobao.com/item.htm?abbucket=15&id=713023764320&ns=1&pisk=gExQMD2T4WVByIGkSBDNCpCCq2I7yAo4O86JnLEUeMIdwF9DN6ko-M81NCd19kkn-aCWtMQk8_5FNg9kGAlq0mJHKgbKgjo26Q07KMBdwaE-elBPeAWLOcSnpgj-gbaa2wmfqI2TmfluWOCGFTELvQIOXt6l2TBd2A1OFt489QdRj36kA9S3-3qTBHOl-UzoKaUMkUNeY4HuITTWMvXnZySiI9xupYUPtgIwLQs8vTERX1BRUzFdpQFOXTBRekEdeOCOFTIRwQI-CdCGFbDLhTgCtpML1GqtaryWQ1Z82h6tZOJQakBDD9_VGpKQ15Mldw1vp1h4jzuVWLbWq8q5PpLDZtdL9j7HeFO1dgiaJip6yI6MvmPCIeJ931pbEuvhAT_A2Nw82dsh6ZKODmF1IFpeyHAQFuBHYn75iNM8qaS90ZLvO8DDBMBJZZxrikfpeKxDuiiaJip6yIT54-rVGpFQPR_0VO1qCAaurhPYPLnf2KfcJOXC7AM_9UV02ur-CANprwBGd1ksCWLl.&priceTId=213e034717402316348515183ef87f&skuId=5164099390355&spm=a21n57.1.hoverItem.5&utparam=%7B%22aplus_abtest%22%3A%223caf3480d45e22ac325d263edcc4fad1%22%7D&xxc=taobaoSearch), which support plenty of joystick. It is easy to use and cheap.

this is my joystick yml file:
[GeekRCwireless.zip](https://github.com/user-attachments/files/18923000/GeekRCwireless.zip)

Start with docs/JOYSTICKS.md and the attached GeekRCwireless.zip, then reproduce the channel mapping in MAVProxy SITL using the reported Futaba T16IZ setup. Compare the joystick's detected channels with the RC channel output; done means channels 5, 7, and 8 respond to the corresponding radio controls without missing or simultaneous changes.

Written by the indexing model from the issue text.