Error: Prepare Queue Full (0x09)

If I try to write a large buffer (>600 bytes or so) with bluepy 1.2.0 with a UD100 on Ubuntu 18.04 I get this error from btmon.

> ACL Data RX: Handle 75 flags 0x02 dlen 27                                                                                                    #202 [hci0] 20.959147
      ATT: Prepare Write Response (0x17) len 22
        Handle: 0x0044
        Offset: 0x01d4
          Data: 313233343536373839313233343536373839
< ACL Data TX: Handle 75 flags 0x00 dlen 27                                                                                                    #203 [hci0] 20.959470
      ATT: Prepare Write Request (0x16) len 22
        Handle: 0x0044
        Offset: 0x01e6
          Data: 313233343536373839313233343536373839
> HCI Event: Number of Completed Packets (0x13) plen 5                                                                                         #204 [hci0] 21.009348
        Num handles: 1
        Handle: 75
        Count: 1
> ACL Data RX: Handle 75 flags 0x02 dlen 27                                                                                                    #205 [hci0] 21.109143
      ATT: Prepare Write Response (0x17) len 22
        Handle: 0x0044
        Offset: 0x01e6
          Data: 313233343536373839313233343536373839
< ACL Data TX: Handle 75 flags 0x00 dlen 27                                                                                                    #206 [hci0] 21.109456
      ATT: Prepare Write Request (0x16) len 22
        Handle: 0x0044
        Offset: 0x01f8
          Data: 313233343536373839313233343536373839
> HCI Event: Number of Completed Packets (0x13) plen 5                                                                                         #207 [hci0] 21.209341
        Num handles: 1
        Handle: 75
        Count: 1
> ACL Data RX: Handle 75 flags 0x02 dlen 9                                                                                                     #208 [hci0] 21.259004
      ATT: Error Response (0x01) len 4
        Prepare Write Request (0x16)
        Handle: 0x0044
        Error: Prepare Queue Full (0x09)

Is this a bug or expected behaviour (ie, the device just doesn't support sending more data)? Is there a way to work around it?

Thanks

EDIT:

I do know that each packet can only be 22 bytes, but my reading of the large writes specification says that you should be able to bundle large writes into "prepared writes" which seems to be what is happening here. The question I have is if it is possible to flush the prepared writes then continue to prepare more writes (I want to avoid having to write a custom data paging protocol - ie, sending the number of pages, then each page one at a time - if possible).

IanHarvey / bluepy

Error: Prepare Queue Full (0x09) #322