iPhone 14 incorrectly combines SMS parts from different message sessions

We are writing to bring to your attention an issue observed

on an iPhone 14 (running the latest iOS version) involving the handling of

multipart (concatenated) SMS messages.

Issue Description:

On two different dates, a handset received two separate A2P

SMS messages, each consisting of two parts:

1. On 15th July, a two-part message was delivered and

correctly displayed as a single combined message.

2. On 18th July, a different two-part message was again delivered and correctly

displayed as expected.

However, in addition to these two correctly displayed messages, the handset

unexpectedly displayed a third message. This third message was a combination of

Part 1 of the 15th July message and Part 2 of the 18th July message, leading to

message content corruption and user confusion.

Preliminary Technical Analysis:

All four SMS parts contained User Data Headers (UDH) for

message concatenation.

It was observed that the Message Reference ID in the UDH was the same across

both messages (i.e., same reference number used for both the 15th and 18th July

messages).

The handset appears to have used the matching Message Reference ID to combine

SMS parts, without validating timestamps or delivery context.

This led to incorrect concatenation across two unrelated messages delivered on

different days.

Request for Vendor Support:

We request your technical team's input on the following:

1. Is the handset expected to cache and use UDH reference

IDs across multiple days without checking message timestamps or session

boundaries?

2. Does the current SMS stack implementation support logic to prevent

inter-message concatenation when parts with the same UDH reference are

delivered across different message sessions or timeframes?

3. Could a software update or patch be made to discard old UDH context or

better isolate multipart message sessions to avoid such mis assembly.

[Re-Titled by Moderator]

Original Title: On two different dates, a handset received two separate A2P SMS messages, each consisting of two parts: 1. On 15th July, a two-part message was delivered and correctly displayed as a single combined message. 2. On 18th July, a different two-part mess